A fresh set of 20 random questions is generated every time you open this page and every time you refresh it.For each of the following multiple choice questions, choose the most appropriate answer :
1. When a monochromatic point source of light is at a distance of 0.2 m from a photocell, the cutoff voltage and the saturation current are respectively Vo = 0.6 volt and is = 18.0 mA. If the same source is placed 0.6 m away from the photocell, then
A. Stopping potential Vo = 0.2 volt and saturation current is = 18.0 mA
B. Stopping potential Vo = 0.6 volt and saturation current is = 18.0 mA
C. Stopping potential Vo = 0.6 volt and saturation currenl is = 2.0 mA
D. Stopping potential Vo = 0,2 volt and saturation current is=2.0mA
2. A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a
A. concave mirror of focal length 10 cm
B. concave mirror of focal length 60 cm
C. concave mirror of focal length 40 cm
D. convex mirror of focal length 10 cm
3. The minimnm potential difference between the base and emitter reqnired to swltch a silicon transistor ‘ON’ is approximately
A. 1 V
B. 3V
C. 5V
D. 4.2V
4. A concrete sphere of radius R has a cavity of radius r which is packed with sawdust. The relative densities of concrete and sawdust are 2.4 and 0.3 respectively. For this sphere to float with its entire volume submerged under water, the ratio of the mass of concrete to the mass of sawdust will be
A. zero
B. 3
C. 4
D. 8
5. A gas mixture consists of 2 moles of oxygen and 4 moles of argon at temperature T. Neglecting all vibrational modes, the total internal energy of the system is
A. 11RT
B. 9RT
C. 15RT
D. 4RT
6. Blue colour of sky is due to
A. Interference
B. Scattering of light
C. Dispersion of light
D. Sun emits more of blue
7. Two particles of mass M and m are moving in a circle of radii R r. If their time-periods are same, what will be the ratio of their linear velocities?
A. MR:mr
B. M:m
C. R:r
D. 1:1
8. In short wave communication waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density 1011 per m-3?
A. 2 MHz
B. 10 MHz
C. 12 MHz
D. 18 MHz
9. A second's pendulum is mounted on a rocket. lts period of oscillation decreases when the rocket
A. Moves up with uniform acceleration
B. Moves up with a uniform velocity
C. Comes down with uniform acceleration
D. Moves round the earth in a geostationary orbit
10. When a compact disc is illuminated by a source of while light, coloured ‘lones’ are observed. This is due to
A. Dispersion
B. Diffraction
C. interference
D. Refraction
11. For a wave propagating in a medium, identify the property that is independent of the others
A. Velocity
B. Wavelength
C. Frequency
D. None. All these are interdependant
12. If an electron and a photon propagate in the form of waves having the same wavelength, it implies that they have the same
A. Energy
B. Momentum
C. Velocity
D. Angular momentum
13. Characteristic X-rays are produced due to
A. Transfer of momentum in collision of electrons with target atoms
B. Transition of electrons from higher to lower electronic orbits in an atom
C. Heating of the target
D. Transfer of energy in collision of electrons with atoms in the target
14. A horizontal platform is rotating with uniform angular velocity around the vertical axis passing through its centre. At some instant of time a viscous fluid of mass m is dropped at the centre and is allowed to spread out and finally fall. The angular velocity during this period
A. increases contmuously
B. remams unaltered
C. decreases continuously
D. decreases initially and increases again
15. Two rods of the same length and material transfer a given amount of heat in 12 seconds when they are joined end to end. But when they are joined length-wise, they will transfer the same amount of heat, in the same conditions, in
A. 1.5s
B. 48s
C. 24s
D. 3s
16. The velocity with which a projectile must be fired so that it escapes earth's gravitation does not depend on
A. Mass of the earth A
B. Mass of the projectile
C. Radius of the projectile's orbit
D. Gravitational constant
17. Parsec is the unit of
A. time
B. frequency
C. distance
D. angular acceleration
18. A six pole generator with fixed field excitation develeps an emf of l00V, when operating at 1500 rpm. At what speed must it rotate to develop 120V?
A. 1200 rpm
B. 1800 rpm
C. 1500 mm
D. 400 mm
19. A stone tied with a string, is rotated in a vertical circle. The minimum speed with which the string has to be rotated ?
A. is independent of the mass of the stone
B. is independent of the length of the string
C. decreases with increasing mass of the stone
D. decreases with increasing in length of the string
20. An object is thrown upward with a vertical velocity of 128 ft./sec. It will return in
A. 64 secs
B. 16 ses
C. 8seconds
D. 4seconds
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