#### Quarterly Exam Model One Mark Questions

12th Standard EM

Reg.No. :
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Physics

Time : 01:00:00 Hrs
Total Marks : 50
50 x 1 = 50
1. Which charge configuration produces a uniform electric field?

(a)

point Charge

(b)

infinite uniform line charge

(c)

uniformly charged infinite plane

(d)

uniformly charged spherical shell

2. An electric field $\vec { E } =10x\hat { i }$ exists in a certain region of space. Then the potential difference V = Vo – VA, where Vo is the potential at the origin and VA is the potential at x = 2 m is:

(a)

10 J

(b)

-20 J

(c)

+20 J

(d)

-10 J

3. Two points A and B are maintained at a potential of 7 V and -4 V respectively. The work done in moving 50 electrons from A to B is

(a)

8.80 × 10-17 J

(b)

-8.80 × 10-17 J

(c)

4.40 × 10-17 J

(d)

5.80 × 10-17 J

4. In electrostatics if the charges are in motion, another force named __________ comes into play in addition to coulomb force

(a)

Lorentz force

(b)

Repulsive force

(c)

Attractive force

(d)

electromagnetic force

5. The value of constant 'K' in coulomb law is

(a)

0.9 x 109 Nm2 C2

(b)

9 x 10-9 Nm2C2

(c)

9 x 109 Nm-2 C-2

(d)

9 x 109 Nm2 C-2

6. The given figure is a plot of lines of force due to two charges q1 & q2 find out the sign of charges

(a)

both negative

(b)

both positive

(c)

upper positive and lower negative

(d)

upper negative and lower positive

7. An uncharged metal sphere is placed between two equal and oppositely charged metal plates. The nature of lines of force will be

(a)

(b)

(c)

(d)

8. Eight mercury droplets having a radius of 1 mm and charge of 0.066 pC each merge to form one droplet. Its potential is

(a)

2.4 V

(b)

1.2 V

(c)

3.6 V

(d)

4.8 V

9. Two condensers (capacitors) of capacity C1 and C2 are connected in parallel. A charge Q given to then is shared. The ratio of the charges Q is

(a)

$\frac { { C }_{ 2 } }{ { C }_{ 1 } }$

(b)

$\frac { { C }_{ 1 } }{ { C }_{ 2 } }$

(c)

C1.C2

(d)

$\frac { 1 }{ { C }_{ 1 }\times { C }_{ 2 } }$

10. The magnitude of torque on dipole is maximum if

(a)

θ=0o

(b)

θ=90o

(c)

θ=180o

(d)

θ=180o

11. The unit for electric susceptibility is

(a)

Nm2 C-2

(b)

C2 N-1 m-2

(c)

C-2Nm2

(d)

N-1 m-2C2

12. In a parallel plate capacitor of capacitance C, a metal sheet is inserted between the plates, parallel to them. The thickness of the sheet is half of the separation between the plates. The capacitance now becomes

(a)

2C

(b)

$\frac{C}{4}$

(c)

4C

(d)

$\frac{C}{2}$

13. Charge Q on a capacitor varies with voltage Vas shown in graph, where Q is along X-axis and V along Y-axis. The area of triangle OAB represents

(a)

capacitance

(b)

capacitive reactance

(c)

magnetic field between the plates

(d)

energy stored in the capacitor

14. Capacitors use the principle of ________.

(a)

self induction

(b)

mutual induction

(c)

electrostatic induction

(d)

dielectric polarisation

15. The electric field intensity at a short distance r from uniformly charged infinite plane sheet of charge is

(a)

proportional to r

(b)

proportional to $\frac{1}{2}$

(c)

proportional to $\frac{1}{r^2}$

(d)

independent of r

16. Two wires of A and B with circular cross section made up of the same material with equal lengths. Suppose RA = 3 RB, then what is the ratio of radius of wire A to that of B?

(a)

3

(b)

$\sqrt3$

(c)

$\frac{1}{\sqrt3}$

(d)

$\frac{1}{3}$

17. The temperature coefficient of resistance of a wire is 0.00125 per °C. At 300 K, its resistance is 1 Ω. The resistance of the wire will be 2 Ω at

(a)

1154 K

(b)

1100 K

(c)

1400 K

(d)

1127 K

18. In Joule’s heating law, when I and t are constant, if the H is taken along the y axis and I2 along the x axis, the graph is

(a)

straight line

(b)

parabola

(c)

circle

(d)

ellipse

19. How many 160 $\Omega$ resistor in parallel are required to carry a current of 5 A on a 100 V line?

(a)

2

(b)

4

(c)

6

(d)

8

20. A potential difference is applied an the ends of a metallic wire. If the potential difference is doubled, the drift velocity

(a)

will be doubled

(b)

will be halved

(c)

(d)

will remain unchanged

21. The thermistors are usually made of

(a)

metals with low temperature coefficient of resistivity

(b)

metals with high temperature coefficient of resistivity

(c)

metal oxides with high temperature coefficient of resistivity

(d)

semi conducting materials with low temperature coefficient of resistivity

22. A potential of 1 kV is applied between the ends of conductor of length 20 cm. The drift velocity of electron in this field is 3.52 x 106 m/s. The relaxation time for the freeelectrons is

(a)

2 nano sec

(b)

4 nano sec.

(c)

6 nano sec

(d)

8 nano sec.

23. The temperature coefficient of resistance increases for the metals when________

(a)

the temperature increases

(b)

the temperature decreases

(c)

does not depend upon the temp~rature

(d)

either (a) or (b)

24. Potentiometer is an instrument used for the measurement of____________

(a)

current

(b)

resistance

(c)

capacitance

(d)

potential difference

25. A wire of length l carries a current I along the Y direction and magnetic field is given by $\vec { B } =\frac { \beta }{ \sqrt { 3 } } =(\hat { i } +\hat { j } +\hat { k } )T.$ The magnitude of Lorentz force acting on the wire is

(a)

$\sqrt { \frac { 2 }{ \sqrt { 3 } } } \beta Il$

(b)

$\sqrt { \frac { 1 }{ \sqrt { 3 } } } \beta Il$

(c)

$\sqrt { 2 } \beta Il$

(d)

$\sqrt { \frac { 1 }{ 2 } } \beta Il$

26. The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenonid to demagnetize the ferromagnet completely is

(a)

1.00 m A (milli ampere)

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

27. Two short bar magnets have magnetic moments 1.20 Am2 and 1.00 Am2 respectively. They are kept on a horizontal table parallel to each other with their north poles pointing towards the south. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centers is (Horizontal components of Earth’s magnetic induction is 3.6 x 10-5 Wb m-2 )

(a)

3.60 × 10-5 Wb m-2

(b)

3.5 × 10-5 Wb m-2

(c)

2.56 × 10-4 Wb m-2

(d)

2.2 × 10-4 Wb m-2

28. Cyclotron is used to

(a)

accelerate charged particles or ions to low voltages

(b)

decelerate charged particles or ions to high voltages

(c)

accelerate charged particles or ions to high energies

(d)

accelerate charged particles or ions to high voltages

29. Melting point of tungsten is about heating element.

(a)

3830°C

(b)

2380°C

(c)

3380°C

(d)

3803°C

30. When the hot and cold junctions of a thermo couple are interchanged then the thermo emf

(a)

increases

(b)

remain unchanged

(c)

decreases

(d)

increases or decreases according to nature of metals used

31. Bohr magneton is given by the formula

(a)

$\frac { neh }{ 4\pi m }$

(b)

$\frac { meh }{ 4\pi }$

(c)

$\frac { 4\pi m }{ en }$

(d)

$\frac { 4\pi e }{ mh }$

32. Fuse wire is an alloy of

(a)

(b)

tin and copper

(c)

(d)

33. To draw thermo electric diagrams Lead is used as one of the metals to form a thermo couple with other metal because _______

(a)

It is a hard metal

(b)

It has high nuclear density

(c)

It does not allow X-rays

(d)

It has zero Thomson effect

34. A moving coil galvanometer shows a deflection of 10° for a current of 0.7 mA. For another current, if the deflection is 15°, then the value of current is ______

(a)

10.5 mA

(b)

1.05 mA

(c)

0.35 mA

(d)

3.5 mA

35. $\frac{20}{\pi^2}H$inductor is connected to a capacitor of capacitance C. The value of C in order to impart maximum power at 50 Hz is

(a)

50 μF

(b)

0.5 μF

(c)

500 μF

(d)

5 μF

36. The unit henry can also be written as

(a)

VS A-1

(b)

Wb A-1

(c)

Ωs

(d)

all

37. If two coils are wound on a soft iron core the mutual induction is

(a)

small

(b)

very large

(c)

infinity

(d)

zero

38. The quantity that changes with time in an A.C current is

(a)

magnitude

(b)

direction

(c)

both magnitude and direction

(d)

none

39. The voltage drop across the resistor in a LCR series circuit is __________________

(a)

VR = IR

(b)

VR = IR2

(c)

VR = I/R

(d)

VR=R/I

40. If the magnetic monopole exists, then which of the Maxwell’s equation to be modified?.

(a)

$\oint { \vec { E } .d\vec { A } } =\frac { { Q }_{ enclosed } }{ { \in }_{ 0 } }$

(b)

$\oint { \vec { E } .d\vec { A } }$=0

(c)

$\oint { \vec { E } .d\vec { A } } ={ \mu }_{ 0 }{ I }_{ enclosed }+{ \mu }_{ 0 }{ \in }_{ 0 }\frac { d }{ dt } \oint { \vec { E } .d\vec { A } }$

(d)

$\oint { \vec { E } .d\vec { l } } =-\frac { d }{ dt } { \Phi }_{ B }$

41. Which of the following E.M waves has the longest wavelength?

(a)

(b)

IR

(c)

X-rays

(d)

visible

42. The wavelength of electromagnetic wave produced by Hertz experiment was

(a)

6mm

(b)

60m

(c)

6000 mm

(d)

60 cm

43. The speed of electromagnetic waves in free space is ______ m/s

(a)

3 x 10-18

(b)

6.2 x 105

(c)

3 X 108

(d)

5 x 102

44. ______ are used in weather forecasting.

(a)

IR photographs

(b)

Microwaves

(c)

(d)

Visible light

45. Continuous spectrum depends only on the _________ of the source.

(a)

characteristic

(b)

temperature

(c)

density

(d)

volume

46. Carbon arc produces ________ spectrum.

(a)

characteristic

(b)

line

(c)

band

(d)

continuous

47. The absorption spectra are characteristic of the __________.

(a)

source

(b)

absorbing substance

(c)

time of travel from source to screen

(d)

spectrometer used to study the spectrum

48. A pure green glass plate when, placed in the path of white light, absorbs________.

(a)

everything

(b)

everything except green

(c)

nothing

(d)

only red

49. If white light is passed through iodine vapour, ________ are obtained.

(a)

continuous absorption spectra

(b)

continuous emission spectra

(c)

band absorption spectra

(d)

emission spectra

50. The spectrum obtained from the photosphere of the sun is of ________ type.

(a)

band spectra

(b)

line spectra

(c)

continuous emission spectra

(d)

non-linear spectra