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6.

On a hot summer night, the refractive index of air is smallest near the ground and increases with height from the ground. When a light beam is directed horizontally, the Huygens principle leads  us to  conclude that as it travels, the light beam

A) becomes narrower

B) goes horizontally without any deflection

C) bends downwards

D) bends upwards

7.

A red LED  emits light at 0.1 W uniformly around it. The amplitude  of the electric field  of the light  at a distance of 1m from the diode is

A) 1.73 V/m

B) 2.45 V/m

C) 5.48 V/m

D) 7.75 V/m

8.

An inductor (L=0.03H) and a resistor (R= 0.15kΩ) are connected in series to a battery of 15V EMF in a circuit shown below. The key K1  has been kept closed for a long time. Then at t=0, K1   is opened and key K2 is closed simultaneously. At t=1ms, the current in the circuit will be (e5  =150)

A) 100 mA

B) 67mA

C) 6.7 mA

D) 0.67mA

9.

A rectangular loop of sides 10 cm and 5 cm carrying a current I of 12A is placed in different orientations as shown in the figures below.

If there is a uniform magnetic field of 0.3 T in the positive z-direction in which orientations the loop would be in (i) stable equilibrium and (ii)  unstable equilibrium?

A) (a) and (b) respectively

B) (a) and (c) respectively

C) (b) and (d) respectively

D) (b) and (c) respectively

10.

Two long current carrying thin wires, both with current I, are held by insulating threads of length L and are in equilibrium as shown in the figure, with threads making an angle θ with the vertical. If wires have mass λ per unit length then, the value of I  is (g= gravitational acceleration)

A) $\sin\theta\sqrt{\frac{\pi \lambda gL}{\mu_{0}\cos\theta}}$

B) $2\sin\theta\sqrt{\frac{\pi \lambda gL}{\mu_{0}\cos\theta}}$

C) $2\sqrt{\frac{\pi g L}{\mu_{0}}\tan\theta}$

D) $\sqrt{\frac{\pi \lambda g L}{\mu_{0}}\tan\theta}$

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