Physics Study Material

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NATA

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JEE MAINS

IMPORTANT QUESTIONS FOR CLASS – XII

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Electrostatics

Q.1 why can one ignore quantization of charge when dealing with macroscopic charges?

Q.2 what orientation of an electric dipole in a uniform electric field corresponds to stable equilibrium?

Q.3 Name the physical quantity whose SI unit is JC^-1.Is it a scalar or a vector quantity?

Q.4 what is the amount of work done in moving 100 µC charge between two points 5 cm apart

on an equipotential surface?

Q.5 The distance of the field point on the axis of a small electric dipole is doubled. By what factor

will the electric field due to the dipole change?

Q.6 In a parallel plate capacitor the potential difference of 10² V is maintained between the plates.

What will be electric field at points A and B.?

. A

. B

Q.7.A Gaussian surface encloses an electric dipole within it. What is the total flux across sphere?

Q.8 What is the angle between the directions of electric field at any (i) axial point

and(ii)equatorial point due to an electric dipole?

Q9. The given graph shows that the variation of charge versus potential difference V for the two

capacitors C1 & C2. The two capacitors have same plate separation but the plate area of C2 is

doubled than that of C1.Which of the line in the graph corresponds to C1 &C2 and why?

Q10. A point charge q is placed at O as shown in the figure.

Is V_P-V_Q +ve or –ve when (i) q>0, (ii) q<0? Justify your answer.

Q11. Why does the electric field inside a dielectric decrease when it is placed in an external electric field?

Q12. A charged particle is free to move in an electric field. Will it always move along an electric line of force?

Q13. If V (=q/4πεor) is the potential at a distance r due to a point charge q, then determine the electric field

due to a point charge q, at a distance r.

Q14. Draw an arrangement of three point charges separated by finite distances, that has zero electric

Potential energy.

Q15. Charge of 2C is placed at the centre of a cube of volume 8 cm³. What is the electric flux passing

through one face?

Three charges, each equal to +2C are placed at the corners of an equilateral triangle.

If the force between any two charges be F, then what will be the net force on either Charge?

Q16. A charged particle q is shot towards another charged particle Q which is fixed, with a speed v. It

approaches Q up to a closest distance r and then returns. If q were given a speed 2v,then find the

closest distance of approach.

Q17. Two capacitors of capacitance 6mF and 12mF are connected in series with the battery .The voltage

across the 6mF capacitor is 2 volt .Compute the total battery voltage.

Q18. Five identical capacitors, each of capacitance C are connected between points X and

Y as shown in the figure. If the equivalent capacitance of the combination between X and Y is 5mF.

Calculate the capacitance of each capacitor.

Q19. A parallel plate capacitor with air between the plates has a capacitance of 8 pF . The separation

between the plates is now reduced by half and the space between them is filled with a medium of

dielectric constant 5. Calculate the value of capacitance of parallel plate capacitor in second case.

Q20. A uniform electric field of 2 kNC^-1 is in the x-direction. A point charge of 3 μC initially at rest at the

origin is released. What is the kinetic energy of this charge at x = 4m?

Q.21. Two identical metal plates are given the charges Q₁ and Q₂ (Q₂< Q₁) respectively. If they are now

brought close together to form a parallel plate capacitor with capacitance C then what is the potential

difference between them?

Q22. Three charges Q, +q and +q are placed at the vertices of a right angle isosceles triangle as shown.

Find the magnitude of Q for which net electrostatic energy of the configuration is zero.

Q.23. A charge Q is distributed over the two concentric hollow spheres of radii ‘r’ and ‘R’(R>r) such that

the surface densities are equal. Find the potential at the common centre.

Q.24. An electric dipole is held in an uniform electric field. Using suitable diagram, show that it doesn’t

undergo any translatory motion, and (ii)Derive an expression for torque acting on it and specify its direction.

Q25. The field potential inside a charged ball depends only on the distance from its centre as

V=ar²+b, where a and b are constants. Find the space charge distribution r(r) inside the ball.

Q26. Four charges each having charge ‘q’ are along x-axis at x=1 cm ,x=2 cm, x=4 cm,x=8 cm .

Find the electric field at x=0 due to these charges.

A 4µF capacitor is charged by a 200V supply. The supply is then disconnected and the charged capacitor is connected to another uncharged 2µF capacitor. How much electrostatic energy of the first capacitor is lost in the process of attaining the steady situation?

Q27.The electric field in a region is radially outward and varies with distance r as E=250 r Vm^-1.Calculate the charge contained in a sphere of radius 0.2 m centered at the origin.

Q28.How charge given to inner sphere transfers to outer sphere? Name the device where it is used. Explain with diagram working of that device

State gauss’s theorem. Use it to find electric field due infinite line of charge. What is the effect on electric field, when charge density gets double and distance between point and line of charge is half.

Q.29 There is an isolated parallel plate capacitor of capacitance C charged to a potential difference V.If the separation between the plates is doubled, how the following quantities will vary:

(i) Capacitance

(ii)Potential difference

(iii) Charge on the capacitor

(iv) Electric field inside the plates

(v) Energy stored.

What is an electric field? Find an expression for electric field along the axial line of electric field. Give its SI unit.

Q.30 What is an electric polarization of a dielectric? What is the effect on capacitance of a capacitor when a dielectric of width‘t’is placed between the two plates of parallel plate capacitor?

What is electric potential? Give its SI unit. Find the expression for the electric potential at any point due to a point charge.

RAY OPTICS

1	Does critical angle depend on wavelength used?
2	Name the phenomenon responsible for mirage formation.
3	Does a prism displace or deviate an incident ray?
4	What are the factors on which light reflected from a surface depends?
5	A thin prism of 60⁰ gives deviation of 30⁰. What is the refractive index of the material of the prism?
6	For what angle of incidence the lateral shift produced by a parallel sided glass slab is maximum?
7	What will be the colour of the sky in the absence of atmosphere?
8	You are provided with four lenses of focal lengths 1cm, 3cm, 10cm and 100 cm . Which two would you prefer for a microscope and which two for a telescope?
9	How deep will a 4m tank appear when seen in air due to optical illusion. Refractive index of water is 4/3.
10	Name the colour having the ( i ) minimum speed ( ii ) maximum speed through a prism.
11	What do you mean by spherical aberration of a mirror ? How can it be minimized?
12	Yellow light of wavelength 589nm is incident on a boundary separating air and glass . Find the speed , wavelength and frequency for ( i ) reflected light ( ii ) refracted light . Refractive index of glass for yellow light is 1.5
13	Two thin lenses having focal lengths having focal lengths +20cm and -30cm are put in contact . The doublet behaves as an achromatic lens. Find the focal length of this doublet. What will be the converging power if the focal length of the two lenses I s made the same?
14	Derive mirror formula for concave mirror forming virtual image.
15	(i )The refractive index of glass is 1.5. What is the time taken by light to travel 1m thickness of the glass ?the speed of light in vacuum is 3x 10⁸ m/s .
16	Where should an object be placed from a converging lens of focal length 20cm so as to obtain a real image of magnification 2?
17	Show that angle of deviation depends on angle of incidence.
18	Write the difference between dispersive and non dispersive medium with examples.
19	Show that lateral displacement is directly proportional to t and i₁.
20	What is the main requirement in the fabrication of optical fibres? How it can be achieved? Write two examples
21	Obtain a relation for refraction from a rarer to denser medium at a convex spherical surface forming real image.
22	Derive thin lens formula for a concave lens .
23	What is myopia? What are its causes? How can it be corrected?
24	Describe an astronomical telescope .Derive an expression for its magnifying power when final image is at ( a ) infinity ( b ) at D
25	Compound microscope has an objective lens of focal length 2cm and eye lens of focal length 5cm. If an object is placed 3cm from the objective and final image is formed at the least distance of distinct vision, find the magnification produced.
26	A double convex lens made of glass of refractive index 1.5 has both curvatures of radii 20cm. An object 2cm high is placed 2cm from this lens , find the position, nature and size of the image.
27	The angle of minimum deviation for yellow light in a prism of refractive index 1.6 is found to be 46⁰. Calculate refracting angle of the prism.
28	Derive lens makers formula.
29	Give the construction and working of a compound microscope. Define and derive an equation for its magnifying power.
30	For refraction through prism derive prism formula.

WAVE OPTICS

1. What is the polarizing angle of a medium of refractive index 1.732?

2. Sketch the variation of intensity of interference pattern in Young’s double slit experiment.

3. What is the ratio of fringe width of bright and dark fringes in Young’s double slit experiment?

4. What is the effect on interference fringes in Young’s double slit experiment if one slit is covered?

5. A polarizer and analyzer are so oriented that intensity of transmitted light is maximum. If the analyzer is rotated through 60⁰ what fraction of maximum light is transmitted?

6. Draw a graph showing variation of intensity of polarized light transmitted by an analyzer.

7. Bubbles of a colourless soap solution appear colored in sun light. Why?

8. What happens to the energy at destructive interference in interference pattern?

9. What will be the effect on interference fringes in Young’s double slit experiment if (i) Monochromatic source is replaced by white light; (ii) Screen is moved away from the slit. Justify your answer.

10. Name one device for producing polarized light. Two polarides are [laced perpendicular to each other and the transmitted intensity is zero. What happens when one more Polaroid is placed between these two at an angle of 45⁰?

11. In Young’s experiment the width of the fringes obtained with light of wavelength 6000 A⁰ is 2mm. What will be the fringe width if the apparatus is immersed in a liquid of refractive index 4/3?

12. Show that the maximum intensity in interference pattern is four times the intensity due to each slit.

13. In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of central diffraction band?

14. How does the resolving power of a microscope change on (i) decreasing the wavelength of light (ii) decreasing the diameter of the objective lens?

15. Draw the wavefront for a beam of light (i) coming from a convex lens when a point source is placed at its focus (ii) divergent radially from a point source.

16. The refractive index of a denser medium is 1.732. Calculate (i) Polarising angle of the medium (ii) angle of refraction.

17. Determine the angular separation between the central maximum, and first order maximum of diffraction pattern due to a single slit of width 0.25mm.

18. State two conditions for sustained interference of light. Draw the variation of intensity with position in Young’s double slit experiment.

19. State Huygens principle. For reflection of plane wavefront at a plane reflecting surface, construct the corresponding reflected wavefront. Using this diagram prove that angle of incidence is equal to angle of reflection.

20. Two independent sources of light cannot be coherent. Why? Two coherent sources have intensities in the ratio 25:16. Find the ratios of the intensities of maxima to minima after interference.

21. In a single slit diffraction experiment width of the slit is made double the original width. How does it affect the size and intensity of central diffraction band? Explain. Draw a graph showing variation of intensity with angle in single slit diffraction.

22. What is meant by plane polarized light. What type of waves show the property of polarization? Describe a method to produce plane polarized light.

23. Define polarizing angle. Derive the relation connecting polarizing angle and refractive index of the medium.

24. State Huygens’s principle. Deduce the laws of refraction on the basis of Huygens’s principle.

25. When two narrow slits 2mm apart are illuminated by a light of wavelength 5000 A⁰ the third minima is measured to be 0.5mm from the central maxima on a screen. What is the distance of the screen from the slit?

26. How does the resolving power of a microscope change when (i) the wavelength of the light is increased (ii) the microscope is kept inside water (iii) diameter of the objective lens is doubled?

27. In Young’s double slit experiment when a source of light of wavelength 5000 A0 is used the fringe width obtained is 0.6cm. If the distance between slit and screen is reduced to half what would be the wavelength of source to get a 0.003 m wide fringes.

28. State the essential condition for diffraction of light to occur. The light of wavelength 600nm is incident normally on a slit if width 3mm. calculate the linear width of central maximum when the screen is 3m away from the slit.

29. Explain the phenomenon of diffraction of light at a single slit. Show graphically the variation of intensity with angle in the diffraction pattern. What is meant by the term angular resolution of a telescope?

30. What do you understand by polarization of light? What are plane of polarization and plane of vibration? Explain polarization (i) by scattering (ii) by reflection.

Explain Young’s double slit experiment of interference of light waves. Calculate the path difference between interfering waves and give conditions for maxima and minima. . Get the expression for dark and bright fringes

IMPORTANT QUESTIONS FOR CLASS – X

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1.            Two wires of same material are having length L and 2L. Compare their resistance and    resistivity.
2.            Why are coils of electric toaster and electric iron made of an alloy rather than a pure       metal?
3.            Two wires are of same length and radius but one of them is copper and the other is of iron. Which will have more resistance? (Given the resistivity of copper = 1.62 x 10 -8              ohm meter and resistivity of iron = 10 x 10-8 ohm meter.
4.            Define 1KWh. Give the relation between 1kwh and Joule.
5.            State which has a higher resistance. A 50W or 25W lamp. Also find the ratio of their         resistances.
6.            A wire of resistance 5 Ohm is spent in the form of closed circle. What is the resistance    between 2 points at the ends of any diameter of the circle?
7.            Calculate the amount of charge that would flow in one hour through the element of an                electric iron drawing a current of 0.4 amps.
8.            A electric toaster of resistance 20 Ohm takes a current of 5A. Calculate the heat                developed in 30 s.
9.            A bulb is rated at 5V, 100mA. Calculate its (1) Power (2) Resistance
10.          Name two special characteristics of a heater coil.

Short answer questions (3 marks)
1.            Define resistance and resistivity. Give the relation between them. Explain the dependence        of resistance on temperature.
2.            With the help of neat circuit, derive the expression for the equivalent resistance of 3     resistances connected in series.
3.            With the help of neat circuit, derive the expression for the equivalent resistance of 3     resistances connected in parallel
4.            (a ) Draw the circuit consisting of a battery of five 2V cells, 5ohm resistor, 10 ohm             resistor, 15 ohm resistor and a plug key. All connected in series (b) calculate the current passing through the above circuit when key is closed.

5.            Two identical resistors each of resistance 2 Ohm are connected in turn (1) in series (2) in               parallel to a battery of 12 V. Calculate the ratio of power consumed in two cases.
6.            A piece of wire is redrawn by pulling it until its length is tripled. Compare the new            resistance with the original value.
7.            An electric kettle is rated 500W, 200V. IT is used to heat 400 gm of water for 30 secs.       Assuming the voltage to be 220V calculate the rise in temperature of water. Specific               heat capacity of water is 4200 J/Kg ºC.
8.            What is the resistance of a copper wire 20 meters long and 0.81 mm in diameter at 20°?

9. A heater draws 1100 W at 220V. (a) Find the resistance of the heater (b) Calculate the energy in KWh consumed in a week if the heater is used daily for 4 hours.

10. The following three appliances are connected in series to a 120 V house circuit: a toaster, 1200 W; a coffee pot, 750 W; and a microwave, 6.0 × 102 W. If all were operated at the same time, what total current would they draw?

11. Three resistors with values of 3.0 Ω, 6.0 Ω, and 12 Ω are connected in series. What is the equivalent resistance of this combination?

12. Three resistors with values of 4.0 Ω, 6.0 Ω, and 10.0 Ω are connected in parallel. What is their equivalent resistance?

13. Two resistors with values of 6.0 Ω and 12 Ω are connected in parallel. This combination is connected in series with a 4.0 Ω resistor. What is the overall resistance of this combination?

14. A circuit contains a 1.5 volt battery and a bulb with a resistance of 3 ohms. Calculate the current.

15. Two resistors with values of 6.0 Ω and 12 Ω are connected in parallel. This combination is connected in Series with a 2.0 Ω resistor and a 24 V battery. What is the current in the 2.0 Ω resistor?

16.          What is the equivalent resistance for the resistors in the figure below?

17.          What is the equivalent resistance for the resistors in the figure below?

18.         For the circuit shown below find the following,

a. What is the equivalent resistance for the resistors in the figure below?

b. What is the total voltage drop across the entire below circuit?

c. What is the total current in the circuit below?

Long Answer questions (5 marks)
1.            State Ohms law with a neat circuit. Explain how this law can be verified and also plot the               expected v-I graph.
2.            (a)          Differentiate resistance and resistivity
                (b)          the ratio of resistivities of two materials a and b is 1:2, ratio of their length is    3:4 and if the ratio of radii is 2:3 find the ratio of resistance of a and b.

HOTs on AC for class XII

noreply@blogger.com (B.K.Anuragi) — Fri, 26 Dec 2014 13:14:00 +0000

ALTERNATJNG CURRENT (2 Marks)

Q1. Mention the factors on which the resonant frequency of a series LCR-circuit depends. Plot a graph showing variation of impedence of a series LCR-CIRCUIT with the Frequency of the applied a.c. source.

Q2. A 50 W – 100 W electric bulb is to be used on a 200 V - 50 Hz a. c. supply. Calculte the inductance of the lamp so that it may glow with its normal brightness.(Take pie = 3 )

Q3. In an a.c circuit A the current leads the voltage by 30⁰ and in circuit B the current lags voltage by 30⁰. What is the ratio of their power factors?

ALTERNATJNG CURRENT (3 Marks)

Q1. 200V variable frequency a.c source is connected to a series combination of L=5H, C=80 μF, and R=40 Ω Calculate (i) angular frequency of the source to get maximum current in the circuit, (ii) the current amplitude at the resonance and (iii) the power dissipation in the circuit.

Q2. A coil draws a current of 1.0 A and a power of 100 W from an a.c. source of 110 V and 50 Hz. Find the resistance and the inductance of the coil.

Q3. A resistance of 40 Ω is connected to an a.c. source of 220 V, 50 Hz. Find (i) the rms current (ii) the maximum instantaneous current in the resistor and (iii) the time taken by the current to change from its maximum value to the rms value.