# WBJEE Physics Test - 8

## 40 Questions MCQ Test WBJEE Sample Papers, Section Wise & Full Mock Tests | WBJEE Physics Test - 8

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Attempt WBJEE Physics Test - 8 | 40 questions in 60 minutes | Mock test for JEE preparation | Free important questions MCQ to study WBJEE Sample Papers, Section Wise & Full Mock Tests for JEE Exam | Download free PDF with solutions
QUESTION: 1

### An electric motor operates on a 50 volt supply and a current of 12 A. If the efficiency of the motor is 30%, what is the resistance of the winding of the motor

Solution:

V = 50 volt; I = 12 ampere
Total power consumed = 50 x 12 W = 600 W
Since efficiency of motor is 30%, therefore, 70% of power is lost in Joule heating.
If Q is the heat produced, then
Q = 70% of 600 W or Q   600 W = 420 W
Also, Q = I2R
∴ 420 = (12)2R or R = Ω = 2.92 Ω

QUESTION: 2

Solution:
QUESTION: 3

### Photons of energy 1eV and 2.5 eV successively illuminate a metal whose work function is 0.5 eV. The ratio of the maximum speeds of the electrons emitted will be

Solution:
QUESTION: 4

Energy per unit volume for a capacitor having area A and separation d kept at potential difference V is given by

Solution:
QUESTION: 5

Same current is being passed through a copper voltmeter and a silver voltmeter. The rate of increase in weights of the cathode of the two voltmeters will be proportional to

Solution:
QUESTION: 6

If a wire of resistance R is melted and recasted to half of its length, then the new resistance of the wire will be

Solution:
QUESTION: 7

A laser beam is used for carrying out surgery because it

Solution:

As the laser beam is highly monochromatic, directional and coherent, it can be sharply focussed.
Therefore it is used for carrying out surgery

QUESTION: 8

Given three equal resistors, how many different combination of all the three resistors can be made?

Solution:
QUESTION: 9

In the circuit,the galvanometer G shows zero deflection. If the batteries A and B have negligible internal resistance, the value of the resistor R will be

Solution:
QUESTION: 10

A proton is about 1840 times heavier than an electron. When it is accelerated by a potential difference of 1 kV, its kinetic energy will be

Solution:
QUESTION: 11

For a metallic wire, the ratio V/i (V= the applied potential difference, i= current flowing) is

Solution:
QUESTION: 12

Choke coil works on the principle of

Solution:
QUESTION: 13

In an L-R circuit, time constant is that time in which current grows from zero to the value

Solution:
QUESTION: 14

Lenz's law is a consequence of the law of conservation of

Solution:
QUESTION: 15

Which of the following radiations have the least wavelength?

Solution:
QUESTION: 16

A charge is placed at the centre of a cube, the flux emitted through its one face is

Solution:
QUESTION: 17

On moving a charge of 20 C by 2 cm, 2 joule of work is done, then the potential difference between the points is

Solution:

W = QV

QUESTION: 18

Two equal charges q of opposite sign separated by a distance 2a constitute an electric dipole of dipole moment p. If P is a point at a distance r from the centre of the dipole and the line joining centre to this point makes an angle θ with the axis of the dipole, then potential at the point P is given by

Solution:
QUESTION: 19

The capacitance of a parallel plate capacitor becomes 4/3 times its original value if a dielectric slab of thickness t = d/2 is inserted between the plates (where d is separation between the plates). The dielectric constant of the slab is

Solution:
QUESTION: 20

Five equal capacitors connected in series have a resultant capacitance of 4 μ F. The total energy stored in these, when these are connected in parallel and charged to 400V is

Solution:
QUESTION: 21

Two point charges of +4 μC and -6 μC are separated by a distance of 20 cm in air. At what point, on the line joining the two charges from charge +4 μC, the electric potential will be zero?

Solution:
QUESTION: 22

A potential difference of 2V exists across a potentiometer wire of 2m length. When the potential difference across a 2Ω resistance of a second circuit is measured by this potentiometer wire, it amounts to 5mm balancing length. The current in the second circuit is

Solution:

2.5 mA

QUESTION: 23

In β + decay process, the following changes take place inside the nucleus

Solution:
QUESTION: 24

In a chain reaction uranium atom gets fissioned forming two different materials. Then total weight of these put together is

Solution:
QUESTION: 25

Sodium surface is subjected to ultraviolet and infrared radiations separately and the stopping potential of photoelectrons determined. Then the stopping potential is

Solution:
QUESTION: 26

An alpha nucleus of energy bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to

Solution:
QUESTION: 27

An image of the sun is formed by a lens of focal length 30 cm on the metal surface of a photoelectric cell and a photoelectric current (I) is produced. The lens forming the image is then replaced by another of the same diameter but of focal length of 15 cm. The photelectric current in this case is

Solution:
QUESTION: 28

If the luminous intensity of a unidirectional bulb is 100 candela, then total luminous flux emitted from the blub, is

Solution:
QUESTION: 29

A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a

Solution:
QUESTION: 30

In case of a semiconductor which one of the following statements is wrong?

Solution:
QUESTION: 31

Indium impurity in Germanium makes it into a

Solution:
QUESTION: 32

Fermi level in an intrinsic semiconductor lies

Solution:
QUESTION: 33

Platinum and silicon are heated upto 250ºC and after then cooled. In the process of cooling

Solution:
QUESTION: 34

Which of the following, when added as an impurity atom in the silicon, produces n-type semiconductor?

Solution:
QUESTION: 35

In a P-N junction diode

Solution:
QUESTION: 36

A semiconductor is cooled from T₁K to T₂K. Its resistance

Solution:
QUESTION: 37

Which one of the following properties of light does not support wave theory of light?

Solution:
QUESTION: 38

A Nicol prism can be used

Solution:
QUESTION: 39

Inverse square law of intensity (illuminance) is valid for

Solution:
QUESTION: 40

When exposed to sunlight, thin films of oil on water often exhibit brilliant colours due to the phenomenon of

Solution:
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