21.

An inductor (L = 0.03 H) and a resistor (R = 0.15 kΩ) are connected in series to a battery of 15V EMF in a circuit shown. 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 = 1 ms, the current in the circuit will be:
()

• 100 mA

• 67 mA

• 6.7 mA

• 6.7 mA

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

• 1.73 V/m

• 2.45 V/m

• 5.48 V/m

• 5.48 V/m

An LCR circuit is equivalent to a damped pendulum. In an LCR circuit, the capacitor is charged to Q₀ and then connected to the L and R as shown.


If a student plots graphs of the square of maximum charge ( Q_Max²  ) on the capacitor with time (t) for two different values L1 and L2 (L₁ > L₂) of L then which of the following represents this graph correctly? (Plots are schematic and not drawn to scale)

A signal of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. The frequencies of the resultant signal is/are:

• 2005 kHz, and 1995 kHz

• 2005 kHz, 2000 kHz and 1995 kHz

• 2000 kHz and 1995 kHz

• 2000 kHz and 1995 kHz

Match List – I (Fundamental Experiment) with List – II (its conclusion) and select the correct option from the choices given below the list:

• A	B	C
  1	4	3

• A	B	C
  2	4	3

• A	B	C
  2	1	3

• A	B	C
  2	1	3

As an electron makes a transition from an excited state to the ground state of a hydrogen – like atom/ion:

• kinetic energy, potential energy and total energy decrease

• kinetic energy decreases, potential energy increases but total energy remains same

• kinetic energy and total energy decrease but potential energy increases

• kinetic energy and total energy decrease but potential energy increases

Assuming human pupil to have a radius of 0.25 cm and a comfortable viewing distance of 25 cm, the minimum separation between two objects that human eye can resolve at 500 nm wavelength is:

• 1 μm

• 30 μm

• 100 μm

• 100 μm

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:

• goes horizontally without any deflection

• bends downwards

• bends upwards

• bends upwards

A train is moving on a straight track with speed 20 ms^-1 .It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound = 320 ms^-1 ) close to :

• 6%

• 12%

• 18%

• 18%

Monochromatic light is incident on a glass prism of angle A. If the refractive index of the material oft the prism is μ, a ray incident at an angle θ, on the face AB would get transmitted through the face AC of the prism provided