This section contains 10 multiple choice questions. Each question has four choices (a), (b), (c) and (d) out of which ONLY ONE is correct.
1. The input resistance of a silicon transistor is 100 W. Base current is changed by 40 µA which results in a change in collector current by 2 mA. This transistor is used as a common emitter amplifier with a load resistance of 4 kΩ. The voltage gain of the amplifier is
(a) 2000 (b) 3000 (c) 4000 (d) 1000
2. A photon collides with a stationary hydrogen atom in ground state inelastically. Energy of the colliding photon is 10.2 eV. After a time interval of the order of microsecond, another photon collides with same hydrogen atom inelastically with an energy of
15 eV. What will be observed by the detector?
(a) One photon of energy 10.2 eV and an electron of energy 1.4 eV.
(b) Two photons of energy 1.4 eV.
(c) Two photons of energy 10.2 eV.
(d) One photon of energy 10.2 eV and another photon of 1.4 eV.
3. A block of mass 1 kg is attached to one end of spring of force constant k = 20 N m–1. The other end of the spring is attached to a fixed rigid support. This spring block system is made to oscillate on a rough horizontal surface (µ = 0.04). The initial displacement of the block from the equilibirum position is a = 30 cm. How many times the block passes from the mean position before coming to rest? (Take g = 10 m s–2)
(a) 11 (b) 7 (c) 6 (d) 15
4. One end of a uniform rod of length l and mass m is hinged at A. It is released from rest from horizontal position AB as shown in figure. The forceexerted by the rod on the hinge when it becomesvertical is
(a) 3/2 mg (b) 5/2 mg
(c) 3 mg (d) 5 mg
5. An open pipe is suddenly closed at one end with the result that the frequency of third harmonic of the closed pipe is found to be higher by 100 Hz than the fundamental frequency of the open pipe. The fundamental frequency of the open pipe is
(a) 200 Hz (b) 300 Hz (c) 240 Hz (d) 480 Hz
6. A system consists of a uniform charged sphere of radius R and a surrounding medium filled by a charge with the volume density ρ=α/r , where α is a positive constant and r is the distance from the centre of the charge. The charge of the sphere for which the electric field intensity E outside the sphere is independent of r is
a) πR2α b) 4πR2α
c) 2πR2α d) 3πR2α/4
7. In a potentiometer experiment, when three cells A, B and C are connected in series the balancing length is found to be 740 cm. If A and B are connected in series balancing length is 440 cm and for B and C connected in series that is 540 cm. Then the emf of eA, eB and eC are respectively (in volts)
(a) 1, 1.2 and 1.5 (b) 1, 2 and 3
(c) 1.5, 2 and 3 (d) 1.5, 2.5 and 3.5
8. A flat glass slab of thickness 6 cm and refractive index 1.5 is placed in front of a plane mirror. An observer is standing behind the glass slab and looking at the mirror. The actual distance of the observer from the mirror is 50 cm. The distance of his image from himself, as seen by the observer is
(a) 94 cm (b) 96 cm (c) 98 cm (d) 100 cm
9. In the figure shown, AB is a rod of length 30 cm and area of cross-section 1 cm2 and thermal conductivity 336 SI units. The ends A and B are maintained at temperatures 20°C and 40°C respectively. A point C of this rod is connected to a box D, containing ice at 0°C, through a highly conducting wire of negligible heat capacity. The rate at which ice melts in the box is [Assume latent heat of fusion for ice, Lf =80 cal g–1]
(a) 84 mg s–1 (b) 84 g s–1
(c) 20 mg s–1 (d) 40 mg s–1
10. Six resistances each of value r = 6 W are connected between points A, B and C as shown in the figure.