Physics Notes for High School

Effects of Forces

2020-06-09T10:22:00.000+08:00

1. In physics, a force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate, to change its moving direction, shape etc. A force has both magnitude and direction, making it a vector quantity.(1)

2. The usual symbol of force is F and its SI unit is Newton (N).

3. As mentioned, a force will be able to change the shape, size, state of motion, direction of motion, acceleration of an object or body.

4. In our daily lives, the effects of forces can be seen everywhere, from driving a car, pushing a trolley, riding a bicycle, swimming, jumping, flying, gliding, rolling and even when stopping a movement.

5. A force is deemed to be balanced when a forces cancel out each other resulting in net zero force. A good example is during a tug-of-war competition when both sides of the opponents have the same pulling force resulting in no net movement. When this happens the force is said to be balanced.

6. When a balanced force is acting on an object, the object will remain stationary or moving at a constant velocity. E.g car moving at a constant velocity and plane flying with a constant velocity. There is no acceleration.

7. Hence, when a system is in unbalanced force, the object will experience acceleration.

8. Bear in mind that there can be more than two forces acting on a body at a certain time. For example below are the forces acting on a car and plane.

9. The movement of the object depends on the direction of the force / forces that have higher magnitude,

(1) Wikipedia

Application for the principles of momentum conservation

2020-05-25T09:53:00.000+08:00

1. Billiard / Pool game

Billiards game uses a ball to hit other balls into holes. The more momentum the cue ball has the greater the momentum force exerted on the target ball / balls.

2. Water hose

Water that jets out from a firemen hose exerts high backward force, hence firemen needs to hold fast the hose to prevent it from moving.

3. Boat

When rowing a boat, the backward force exerted by the rower will result in the same forward force being produced.

4. Jet engine

The hot gas and vapour ejected at the exhaust of a jet engine will produce an upward and forward force, equal to the force exerted by the hot gas.

5. Rocket

A mixture of oxygen and hydrogen are burned up in the combustion chamber. This creates a very high pressure and force which is expelled at the bottom of the rocket. As a result, an upward force of similar magnitude is produced.

Linear momentum collision problem calculations 2

2020-05-15T13:42:00.003+08:00

Questions

1. A toy truck with a mass of 3 kg was moving at 3 ms^-1 and hit with another toy truck of 1 kg and was moving with a velocity of 1 ms^-1, in the opposite direction. After collision, both trucks moved together in the same direction, calculate the common velocity of the two objects after collision.

m₁u₁+ m₂u_{2 = (}m₁+ m₂₎v
           (3)(3) + (1)(-1) = (3+1)v
            9 – 1 = 4v
           v = 2 ms^-1

2. A hunter shot a 100g bullet from a 1.5kg gun. If the bullet travelled 200 ms-1 after being triggered, what is the backward jerk of the gun. (Think final backward velocity of the gun).

Total initial momentum = Total final momentum = 0
m₁u₁+ m₂u_{2 =}0
1.5(v) + 0.1(200) = 0 ß make sure to convert 100g to kg
1.5v +20 = 0
v = - 13.3 ms-1 ß Value is negative because gun moved in opposite direction

3. A trolley of mass 2 kg was in a stationary condition, before a 5 g sticky plasticine was thrown into it with a velocity of 500 ms-1. After hitting the trolley, the plasticine sticks into it. Calculate the final velocity of both the trolley and plasticine?

Use the classic formula of momentum conservation
m₁u₁+ m₂u₂= m₁v₁+ m₂v₂
0.005 (500) + 2 (0) = (0.005+ 2)v
2.5 = 2.005v
v = 1.245 ms^-1

Linear momentum calculation 1 (Collisions)

2020-05-03T14:14:00.003+08:00

The principle of conservation of momentum:

Total momentum before collision = Total momentum after collision

Inelastic collision

1. An object of mass = 2 kg with initial velocity of 30 m/s hit a stationary object of mass = 4 kg. After the collision, both objects move together with identical velocity. Calculate the final velocity of both objects.

Total momentum before collision

= m₁u₁+ m₂u₂

_{= 2(30) + 4 (0)}

= 60 kg ms^-1

Total momentum after collision = 60 kg ms^-1

= m₁v₁+ m₂v₂

= 2v + 4v

= 6v

Remember

60 kg ms^-1= 6 v

Final velocity for both objects, v = 10 ms^-1

Elastic collision

1. An object of mass (object 1) = 2 kg with initial velocity of 40 m/s hit an object of mass (object 2) =3 kg with initial velocity = 20 m/s. After the collision, object 1 moves with v₁= 30 m/s. Calculate the final velocity for object 2.

Total momentum before collision

= m₁u₁+ m₂u₂

= 2 x 40 + 4 x 20

= 160 kg ms^-1

Total momentum after collision

= m₁v₁+ m₂v₂

= 2 x 30 + 4 v₂

= 60 + 4 v₂

Final velocity of object 2

160 = 60 + 4 v₂

4 v₂ = 100

v₂= 25 ms^-1

3. Object 1 (m₁= 2 kg) moves with initial velocity (u₁= 20 m/s) and hits object 2 (m2 = 1 kg) (u2 = - 5 m/s) which moves in the opposite direction. After the collision, Object 1 moves with velocity = 15 m/s. Calculate the velocity for object 2, assuming that the collision is elastic.

Total momentum before collision

= 2 x 20 + 1 x (-5) negative denotes opposite direction

= 35 kg ms^-1

Total momentum after collision

= 2 x 15 + 1 x v₂

= 30 + v₂

Final velocity of object 2, moving in the same direction

35 = 30 + v₂

v_{2 =}5 m/s

Solving problems, questions, calculations, linear motion 2

2020-04-23T15:11:00.003+08:00

Look at the diagram above. It is a displacement-time graph for a moving object.

Questions:

a) What is the displacement of the object at t = 2 s?

Answer = 20 m

b) When does the object cease to move?

Answer = From t = 4 s until t = 8 s

c) When does the object starts to move in the opposite direction?

Answer = At t = 8 s.

d) What is the velocity of the object at time

i) t = 6 s?

Answer = the object is not moving at all, hence velocity is zero.

ii) t = 9 s?

Gradient of the graph, as t = 9 is in the middle of the movement.

Hence v = - 40 / 2 = - 20 m/s

* Note the negative sign which indicates that the object is moving in the opposite direction.

e) Calculate the total distance traveled?

40m + 80m = 120 m, note that the direction of the movement does not matter here as distance is a scalar quantity.

f) Calculate the total displacement traveled?

+40m = ( - 80m) = -40m

Note that the total displacement is negative indicating the final position is -40m opposite the first direction of travel.

g) What is the average speed of the object?

Average speed = distance / time
= 120 / 12 = 10 m/s

h) What is the average velocity of the object

Average velocity = total displacement / time

= -40 / 12
= 3.33 m/s

Solving problems, questions, calculations, linear motion 1

2020-04-19T13:32:00.000+08:00

1. A car moves in a straight line from a static state to a state of constant acceleration. After 1000 m, the car achieves a velocity of 240 m/s. Calculate

i) the acceleration of the car
ii) time taken
iii) the velocity at t= 2 s.

Answer:

From the question the information we can get is

a = 0 m/s
v = 240 m/s
s = 1000 m

i) For acceleration

We can use the formula v^2 = u^2 + 2as
Refer to (http://fiziknota.blogspot.com/2020/04/linear-motion-formula.html)

^2 is squared

When we rearrange the formula we get

a = (v^2 - u^2) / 2s

= 240^2 - 0^2 / (2 x 1000)

= 28.8 ms^-2

ii) for time

We have to rearrange v = u + at

t = (v - u)/ a

= (240) / 28.8

= 8.33 s

iii) velocity at t = 2 s.

Using v = u + at

v = 0 + (28.8 x 2)

v = 57.6 m/s

Linear Motion Formula

2020-04-19T13:14:00.002+08:00

Below are the common formula for Linear Motion:

Where

v = final velocity
u = initial velocity
s = displacement
a = acceleration
t = time

Generation of Electricity from Nuclear Fission

2020-04-16T20:46:00.001+08:00

Nuclear energy is one of many alternatives of generating electricity. In fact, nuclear energy is primarily used to generate electricity.

Among the uses of nuclear energy are as a method to propel submarine, big vessels and satellites. Engines run by nuclear energy can go on without refuelling for one or two years.

The process of generating electricity is done by nuclear power plant or power station.

The process begins in the nuclear reactor:

i. The nuclear fission of Uranium 235 creates a massive amount of heat energy in the nuclear reactor. The heat of the uranium bundles in the core must be controlled to prevent overheating which can cause the reactor to melt.
ii. This energy is then used for boiling water which transforms it into steam at high pressure and temperature.
iii. This creates a powerful steam energy which rotates the turbines . The cold steam then moves to a condenser, condensed into water and then moves back to the reactor.
iv. The rotating turbines also spins a set of dynamos which produce electricity, this electricity is then further processed, adjusted and transported by cables to consumers.

It is really crucial to keep nuclear power plants in order as any leakage or accident will cause massive environmental and health damage.

Managing radioactive waste

2019-12-01T16:13:00.000+08:00

Radioactive wastes are dangerous. The detrimental effects of radioactive wastes depend on the quantity, type, half-life of the waste and the type of radioactive rays emitted. Radioactive waste with the longest half-life poses the greatest risk to human health.

Radioactive waste can be classed into three main categories low, intermediate and high-level. (https://www.ansto.gov.au/education/nuclear-facts/managing-waste)

Low-level waste requires minimal shielding during, handling, transport and storage. They are made of paper, plastic, cloth and filters which contain a small amount of radioactivity. They are stored in drums and the radioactive emission are measured using a scanning system.

Intermediate-level waste requires additional shielding during handling, transport and storage as they emits higher radiation. They usually comprised of products of radiopharmaceuticals and reactor operations.

High-level waste requires increased shielding and human contact. It also requires cooling system as the waste can generate heat. The waste comes from the operation of nuclear power plants.

There has to be a consensus among countries on the safe disposal of radioactive wastes. For example, ocean disposal is no longer permitted. More information here (https://en.wikipedia.org/wiki/Radioactive_waste).

Radioactive waste can be initially treated by immobilisation of waste through vitrification, ion exchange and synroc method.

Long-term options of radioactive waste management include above-ground disposal, geologic (underground) disposal, re-use, transmutation or space-disposal. Although, not all of the said methods are being currently implemented.

There is also issues associated with illegal dumping of radioactive materials which has caused international concerns.

More information on this topic is available here:
https://ukinventory.nda.gov.uk/about-radioactive-waste/how-do-we-manage-radioactive-waste/
https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-wastes/radioactive-waste-management.aspx

Contributions of electronics

2019-08-19T21:44:00.001+08:00

The development of electronic has occured rapidly during the past century

For instance, 1960s - colour televisions, 1970s - microwave ovens, 1980s - personal computers and internet, 1990s - handphones, 2000s - digital technologies and ICTs.

Examples of contributions of electronics in daily life:

1. Computers
2. Telecomunications
3. Automations
4. Medicines
5. Digital camers.
6. Laptops
7. VCDs
8. MP3 players
9. Traffic light control systems

and many more

More information can be found here:

https://www.codrey.com/dc-circuits/electronics-and-its-applications/
https://hubpages.com/technology/The-Role-of-Electronic-Components-in-Our-Daily-Life
https://www.quora.com/What-are-the-types-of-electronic-devices

Applications of Logic Gates in Control Systems

2019-08-19T21:33:00.000+08:00

Logic gates are made to make decisions based on the inputs obtained, this is when logic gates function as automatic switch.

There are three main components in a control system.

A. Input or Inputs - consist of detectors which are able to detect changes (light, electrical, sound etc)
B. Control circuit - electronic devices (capacitors, diodes and transistors)
C. Outputs - devices (sirens, bulbs, alarm, heater, electric motors)

Some examples are

1. Control system for cooling fans
2. Fire control system
3. Temperature control system
4. Car theft alarm system

https://image.slidesharecdn.com/25-141106225713-conversion-gate01/95/69application-of-logic-gates-4-638.jpg?cb=1415314801

https://www.electrical4u.com/electrical/wp-content/uploads/2013/08/application-of-OR-gate.gif

https://qph.fs.quoracdn.net/main-qimg-186dbb7c7306f00e092e8f110928206c.webp

Analysing Logic Gates

2019-08-19T21:20:00.002+08:00

A logic gate is a switching circuit that is applied in computers and other electronic devices and its a basic electronic building block used in computers and many digital devices.

This logic gate is responsible for performing logical operations in digital systems. The digital system involves two outputs inputs and output which involve two levels of voltage either high (1) or low (0).

The logic gates are named 'gates' because they give a '1' on the output only when a particular combination of 1 and 0 is present at the inputs.

Logic Gates as Switching Circuits

A logic gate is a switching circuit made up of a combination of transistor switches. It has one or more input terminals but only one output terminal. It's useful to find out how come simple logic gates can be built from switches. Normally, a closed switch is considered to be at a high state (1) and and open switch low state (0). Switches in series can perform and AND gate function and switches in parallel can perform and OR gate function.

Types of logic gates:

1. NOT gate
2. AND gate
3. OR gate
4. NAND gate = AND and NOT gates
5. NOR gate = OR and NOT gates

The NOT, AND and OR gates are the three basic logic gates. All other more sophisticated gates are made from these gates by combining these gates in specific ways.

https://physicsabout.com/wp-content/uploads/2018/02/logic-gates-min.png

Applications of Cathode Ray Oscilloscope

2019-08-18T11:37:00.001+08:00

There are several applications of CRO, namely:

1. Measuring the potential difference of a d.c.supply
2. Measuring the potential difference of an a.c. supply
3. Measuring a short duration of time
4. Measuring wave frequency
5. Displaying different wave forms

How energy of electrons is converted in Cathode ray tube

2019-08-18T11:26:00.001+08:00

Below are samples of Cathode ray tube diagram

Reference: https://www.semanticscholar.org/paper/Simulation-of-cathode-ray-tube-Maiti-Rajagopal/ca0d214bf66cd8a3f01d175e0455dcc37deb71f4/figure/0

Reference: https://www.javatpoint.com/fullformpages/images/crt.gif

As electric current pass through the filament, it heats up and emits electron. This means electrical energy is converted to heat energy. The difference in electrical energy potential from anode and cathode increases the acceleration of electrons towards the fluorescent screen. This means electrical potential energy is converted kinetic energy of electrons. The high speed electrons then smash the screen and produce flourescence (light).

So that means electrical potential energy = kinetic energy

eV = 1/2 mv^2

electron charge, e = 1.6 x 10 ^ -19 C
electron mass, m = 9.1 x 10 ^ -31 kg
v = final velocity of electron

v^2 = 2eV/m

Example of question:

KE = 1.2eV

Reference: https://images.slideplayer.com/39/10862668/slides/slide_5.jpg

Resolution of Forces

2015-03-22T14:02:00.000+08:00

We know that two forces when combined together will form a single resultant force. On the other hand, a single force can be divided or broken up into two components.

The reversal of this process is called the resolution of forces. A force is usually resolved into two components that are perpendicular to each other.

A force can be resolved into two component forces graphically or by using trigonometry.

Consider the diagram above. In the diagram the force F is resolved into two perpendicular component forces that is the Fy and Fx components (using parallelogram method).

To calculate the magnitude of the vertical (Fy) and horizontal (Fx) forces, we can use simple trigonometry.

Fx = F cos θ , Since cos θ = (Fx/F)

Fy = F sin θ, Since sin θ = (Fy/ F)

Examples of calculation:

By using the diagram above, Let say F = 80 N and θ = 30 degree

The horizontal component Fx,
= F cos θ
= 80 cos 30
= 80 X 0.866
= 69.3 N to the right

The vertical component Fy,
= F sin θ
= 80 sin 30
= 80 x 0.5
= 40 N upwards

Another example would be as below:

Source: imgkid.com

Another good example:

Source: Physicsclassroom.com

Resultant Force II

2014-12-08T11:23:00.000+08:00

For the resultant force of two perpendicular forces, we need to consider other methods.

In this situation, two non-parallel forces are acting on an object at a right angle to each other.

So with the example above, there is Force a (Sometimes called component a) and Force b (sometimes called component b).

The resultant force is named as F.

The resultant force can be obtained through Phytogras theorem

F^2 = a^2 + b^2

F = Square root of (a^2+b^2)

Example of question:

What is the resultant force if Force a,70N and Force b, 90N act on an object and both for the forces are perpendicular to each other. What is the direction of the force?

i. Resultant force, Fr = Square root of (70^2 + 90^2)
= 114N

ii. Direction, Tan (theta) = 70 / 90
= 0.7778
= 37.9 degree

So the resultant force is 114N and the direction is 37.9 degree from the original 90N force.

If you have known the basic principle.
The questions can be manipulated but you can still know how to work out the question.

Resultant Force I

2014-09-14T10:03:00.000+08:00

1. Resultant force for two parallel forces

How to find the resultant force for two parallel forces?

If the forces are moving in the same direction. The resultant force is also in the direction of both forces. you have to ADD the magnitude of the two forces.

If the forces are moving in opposite direction, The direction of the resultant force is the same as the larger force. Subtract the magnitude of the lesser force by the larger force.

In the above example the resultant force is 1N in the direction of the larger force which is the 4N.

2. Resultant force of Two Non-Parallel Forces

When there are forces that moves in a non-parallel manner, simple calculation cannot be done to find the resultant force. What we can do is draw a scaled diagram.

Either by using the Triangle method

or the Parallelogram method

or more specifically

In the example above, let say if we put 100N = 2 cm.

F2 = 8 cm
F1 = 10 cm

You have to measure the angle carefully using a protractor to measure the angle between the two forces. The resultant force is the R which you can measure using a ruler and convert it back to the actual magnitude (e.g. if the resultant force is 12 cm then it would convert to 600 N)! The angle is the angle between R and F1.

Can you find the resultant force for this one?

Forces in Equilibrium II

2014-09-10T20:02:00.000+08:00

As we have learnt, when forces are in a state of equilibrium, the net force (or also known as resultant force) is zero. The object is either at rest or in a motion with constant velocity (hence zero acceleration).

Examples of two forces in equilibrium are a plate resting on a table or a skydiver falling at a constant velocity which is also known as terminal velocity.

An object that is resting on a tilted or inclined plane also can be in equilibrium with each other. In this case three forces are in equilibrium.

N is the normal reaction.
Weight is represented by mg where m = mass of the object and g is the gravitational constant.

Addition of forces and Resultant Force

In this example, you can see that there are three different ways on how a 40N force and a 30N force can react. In the first example both forces react in the same direction.

In the second example, both forces react in opposite direction. Hence the resultant force will be 10N in the direction of the greater force (40N).

In the third example, The two forces are in perpendicular with each other. If you are using the parallelogram method ( Or Phythagoras theorem!) you can easily find that the resultant force is 50N.

So if it helps, resultant forces can be categorised in three situations:

1. Two parallel forces
2. Two non-parallel forces
3. Two perpendicular forces

at GCE-O level, you may be asked to find the resultant force for only two forces. But in reality or more complex situations there are many forces that act on an object.

Linear Motion Calculation 2

2013-12-09T17:35:00.001+08:00

Linear motion calculation 2

A bike has to move along a straight road. It starts from rest and then moves with uniform acceleration. After moving a distance of 100 m, it achieves a velocity of 120 m s^-1.

Find:

a) the bike acceleration
b) the time taken
c) the bike's velocity when t= 3s

SOLUTION

For question A)

Extract all the information that are needed.

u = 0 m/s
v = 120 m/s
s =100 m

What you need to find is the acceleration.

However there are several linear motion equation that needs to be considered.

1. a = (v -u)/t

2. s = 1/2 (u +v) t

3. s = ut + 1/2(at^2)

4. v^2 = u^2 + 2as

So we choose this equation v^2 = u^2 + 2as, because we have v, u and s.

rearrange the equation, we will get

a = (v^2 - u^2)/2s

= (120^2 - 0^2) / 2 (100)

= 72 m/s^2

For question B)

using a = (v - u) / t

rearrange the equation and you will get

t = (v -u)/ a

= (120 -0) / 72

= 5/3 s

For question C)

we need to find v,

so the equation that is most suitable is

v = u + at

= 0 + 72 (3)

= 216 m/s

Hope everything makes sense!

Linear Motion Calculation Examples

2013-12-08T23:14:00.003+08:00

A bicycle moved from point A and then moved 50 m to the north in 60 seconds. The bicycle then moved 120 m to the east in 40 seconds. Finally, it stopped. Calculate the

1. Total distance moved by the bicycle
2. Displacement
3. Velocity
4. Average speed
5. Speed of the bicycle when it is moving to the north

Solution:

1. Total distance = 50m + 170m
= 170m

2. Displacement

Remember displacement is the shortest distance between two points.

Imagine A as the beginning of a triangle. Then connect it with a line of 50m upwards then it turns left 120m (go east). so the distance is the hypotenuse.

Using Pythagoras' theorem = Squared root (120^2 + 50^2)
= 130m

3. Velocity = Displacement / time

= 130 m / 100 s
= 1.3 m s^-1

4. Average speed of the bicycle = total distance / total time

= 170m/ 100s
= 1.7 m s^-1

5. Speed = distance / time

Distance = 50m, time = 60s

= 50m / 60s

= 0.83 ms^-1

Be careful during calculation as most of the time Physics requires a good skill in maths!!

Experimental Errors

2013-12-08T14:26:00.002+08:00

When doing experiments there are several errors that we need to consider. For example the error when taking reading from instruments and also the influence from the outer surroundings. This is true for all scientific investigations. Even machines have errors! and they do need to be calibrated consistently!

Error is the difference between the measured value and the real or actual value. (The difference in reading is known as the error)

Two main types of error are systematic error and random error.

Systematic error occurs when there is an error when reading the scale that is being used. It is caused by the surroundings, the instrument itself (scale may not be uniform or even blurred due to wear and tear) and of course the observer error.

Systematic error results in the measurement or reading being consistently over the actual value OR consistently smaller than the actual value.

There are several possible causes of systematic error:

One of the most common error is the Zero Error. Zero Error is caused if the reading shown is Not zero when the true value is actually zero. This is most probably caused by a flaw in the instrument for example when using a ruler that has lost its zero scale due to wear and tear hence causing an error in the measurement of length.

Wrong assumptions may also cause error, for example if you assume that water boils at 100 degree celcius but actually its boiling point is higher if there are impurities in it. (Pure water boils at 100 degree celcius)

There is also a possibility to create error when there is a lag of reaction time. For example in a sports day, when measuring a 100 m running time using a stopwatch. The observer may not press the stop button exactly when the foot of the runner touches the finishing line.

Sometimes, as I have mentioned, instruments that are not properly calibrated could also cause error and this has to be put in consideration when writing a report or when there is an anomaly in reading.

Another type of error that needs to be considered is Random Error.

Random error is caused by the observer who reads the measuring instrument. Just like the systematic error, there can exist positive or negative error. Positive error is when the reading is bigger than the real value and negative error is when the reading is smaller than the real value.

One of the ways to reduce random error is to take several readings for a measurement and then taking the average reading to be analysed.

There are several examples of random error.

Miscounting numbers during observation or change in the surrounding due to temperature, wind, light, exposure to chemicals or impurities may cause error. Sometimes the observer may read the scale wrongly (as in the case of reading a scale in on a beaker or ruler (parallax error). Parallax error occurs when a reading is taken from an unsuitable position relative to the scale.

Ways to reduce error

Magnifying glass to enhance the visual of scale on the instrument.
Avoiding parallax error by positioning the instrument (meter rule) properly on the table with the eyes perpendicular to the scale. This also applies when reading other instruments. Parallax error can also be reduced by putting a strip of mirror next to the scale (for example in ammeter), the eye must be positioned so that the image formed on the mirror is fully covered by the indicator hand of the ammeter.

Some instruments can be adjusted to eliminate zero error. For example when using an ammeter, there is an adjuster to set the indicator to zero before making any measurement.

In the case of a ruler, measurement can be carried out starting from the next clear scale for example if scale 0.0cm is blurred, we can start measuring the length from 2.0cm, of course taking the difference of value in consideration when recording the final reading.

Precautionary Steps In Handling Radioactive Substance

2013-04-12T15:20:00.000+08:00

Experiments that involves radioactive substances are conducted in a room surrounded by concrete walls. Strong radioactive substances are handled using remote-controlled mechanical arms from a safe distance.

Weak radioactive substances could be handled by using tweezers.

Radioactive wastes must be disposed off by using suitable and safe methods. Rooms, buildings, containers and radioactive storage places must be labelled with the sign for radioactive substance. Radioactive substances are contained in thick lead containers.

Protective suits and gears such as gloves and eye glasses made of lead are used at all times when handling radioactive substances. These shields protect the workers from harmful radiations.

Workers handling radioactive substances must wear special badges which detect the amount of radiation they are exposed to. Food and drinks are not allowed in places where radioactive substances are handled.

Low level radioactive wastes

Sources: Hospitals, nuclear power stations, industries, research laboratories.
Examples: Contaminated equipments, shoes, biohazard suit, clothing, wrappers, air filters, gloves, etc.
Half-life: Short
Radioactivity level: low
Management: Solid wastes are stored

Intermediate level radioactive wastes

Sources: Nuclear power stations, industries, research laboratories
Examples: Component in nuclear reactors, chemical sediments
Half life: long
Radioactivity level: High
Management: Radioactive wastes are placed in concrete block and then buried underground

High level radioactive wastes

Sources: Nuclear power stations
Examples: Fuel rods used in nuclear power stations
Half life: Long
Radioactivity level: High
Management: Fuel rods are submerged in a pool of water to cool them down. The rods are then stored in a steel container which are buried underground at a depth of between 500m and 600m.

Realising the importance of proper management of radioactive substances

2013-03-27T09:07:00.001+08:00

Negative effects of radioactive substances

Radioactive substances emit radiations that are harmful to living things. This is due to the ionisation and penetrating properties of these radiations.

As the radiations pass through living cells, they ionise the neighbouring atoms or molecules. The reactive ions that are produced will

i. Interfere with the chemical processes in the cell.
ii. Induce mutations in the genetic structure of the cell.

At the same time, the radiations might kill the cell in body tissues. If there are far too many cells that were destroyed, the organism may die.

The amount of damage inflicted to humans depends on the types of radiation, dosage and exposure period, methods of insertion into the body and location of exposure.

i. Types of radiation - Alpha particles outside the body are harmless because they can be stopped by the human skin.

ii. Dosage and exposure - Exposure to high dosage of radiation in a short period of time results in immediate symptoms such as vomitting, increase in body temperature, blood composition change and many more.

iii. Methods of insertion into the body - The internal part of human body can be damaged by alpha particle that were ingested through food or inhaled through air, this is due to the high ionising effect of Alpha particles.

iv. Cells that are actively dividing are more vulnerable to radiations. Skin cells in general can withstand higher dosage of radiation compared to the other internal organ.

The harmful effects of radiation on humans can be divided into two categories which can be categorised as Somatic effect or Genetic effect.

i. Somatic effect: includes damage to all parts of the body except the reproductive organs. Symptoms include: fatigue, vomiting, hair loss, infertility in male, severe skin burn and leukemia or cataracts (which may arise after a long period of time).

ii. Genetic effect: includes damage to reproductive cells. Genetic defect can be passed down to the next generations. Examples of genetic defects include Down Syndrome, Klinefelter Syndrome, Turner Syndrome.

Nuclear Reactor

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1. A nuclear reactor gives massive amount of energy through nuclear fission.

Source: http://avasiyamillai.blogspot.com/2011/07/nuclear-power-plant.html

2. The energy freed from the fusion of nuclear fuel heats the water in the surrounding.

3. Consequently, this produces steam which drives the turbines. The turbines then drive the electrical generators.

4. The table below summarises the main functions of each components.

Component	Function / Explanation
Graphite Moderator	Fast moving neutrons are slowed down by collisions with nuclei in the moderator so that they can cause further fissions. In some nuclear power plant, the moderator is water.
Uranium rod (Fuel)	Fission reactions take place in the uranium rod to create nuclear energy. The uranium used is often ‘enriched’ by increasing the proportion of the isotope uranium-235 above the natural value of 0.7% to 3%.
Control Rod	The rate of the fission reaction is controlled by inserting or withdrawing these rods. The nuclei in the rods absorb neutrons without undergoing any reaction. Sometimes the rod is made of cadmium.
Coolant	To take away heat from the nuclear reactor. Substances with high specific heat capacity such as ‘heavy’ water and carbon dioxide are used.
Thick Concrete Wall	To avoid the run off of harmful radiations.
Steam generator	Water in the generator is heated and changed into steam. The steam then drives the turbines.
Turbines	To revolve the dynamo in the electrical generator to generate electricity

5. Nuclear reactors are used in the production of:

a) High-intensity neutron beams for research
b) Artificial Radioactive Isotopes for medical research
c) Fissionable transuranic elements such as plutonium from uranium-238

Reasons for the use of Nuclear Energy

1. Production of nuclear energy from nuclear fuels involves a decreased cost. A small amount of nuclear fuel can provide a large amount of energy.
2. Nuclear reactors are relatively safe especially with the sophisticated technology constantly developed and improved.
3. The decreasing supply of fossil fuels make it essential for the use of alternative sources of energy.
4. The use of nuclear energy does not release greenhouse gases such as carbon dioxide.

Reasons against the use of Nuclear Energy

1. Radioactive residues from nuclear stations have quite a long half-lives.
2. There is a chance of leakage in the radioactive waste containers placed underground or underwater.
3. High cost of constructing a nuclear power station.
4. Accidents could happen due to human error no matter how sophisticated the technology is and this should be put into consideration.

Nuclear Fusion

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Nuclear fusion occurs when two or more light and small nuclei come together to perform a heavier nucleus.
This process is accompanied by the release of a huge amount of energy.

For example

Deuterium + Tritium = Helium + neutron + (Energy)
(2H1) + (3H1) = (4He2) + (1n0) + Energy

It is far more difficult to achieve fusion than fission due to the nature of the hydrogen nuclei that repel each other. In order to let this happen, the nuclei should be heated up to 10^8 K or more so that the nuclei will have enough kinetic energy to overcome the electrical repulsion between the nuclei.

The Sun acquires its energy from the fusion of hydrogen nuclei.

- Deuterium clashes with tritium to form a helium nucleus at a high temperature. This is accompanied by the release of a neutron and mass defect. The mass defect produces a massive amount of energy.

A hydrogen bomb also uses the principle of nuclear fusion for its design.