Q. The existence of electromagnetic waves were experimentally confirmed by:

1. Faraday
2. Hertz
3. Maxwell
4. Tesla

Q. The resonant frequency of an L-C circuit is

1. $\frac{1}{2\pi \sqrt{LC}}$
2. $\frac{1}{2\pi }\sqrt{\frac{L}{C}}$
3. $\frac{1}{2\pi }\sqrt{\frac{C}{L}}$
4. $\frac{1}{4\pi }\sqrt{\frac{L}{C}}$

Q. Power consumed in an AC circuit becomes zero if

1. inductance and resistance are both high.
2. inductance and resistance are both low.
3. inductance is low and resistance is high.
4. inductance is very high and resistance is negligible.

Q. The Q-factor of a resonant circuit is equal to

1. $\frac{1}{L}\sqrt{\frac{R}{C}}$
2. $\frac{1}{R}\sqrt{\frac{L}{C}}$
3. $\frac{1}{RL}\sqrt{C}$
4. $\frac{1}{C}\sqrt{\frac{R}{L}}$

Q. Two different coils have self inductance $8mH$ and $2mH$. The current in both coils are increased at same constant rate. The ratio of the induced emf's in the coil is :

1. $4:1$
2. $1:4$
3. $1:2$
4. $2:1$

Q. The frequency of radio waves corresponding to a wavelength of $10m$ is

1. $3\times {10}^{9}Hz$
2. $3.3\times {10}^{8}Hz$
3. $3\times {10}^{7}Hz$
4. $3\times {10}^{-7}Hz$

Q. Which of the following is not an electromagnetic wave?

1. Light rays
2. X-rays
3. Alpha rays
4. Gamma rays

Q. The electromagnetic waves travel in free space with the velocity of

1. Sound
2. Greater than that of sound
3. Light
4. Greater than that of light

Q. The power factor is an L-C-R circuit at resonance is

1. $0$
2. $1$
3. $0.8$
4. $\frac{1}{2}$

Q. An inductor may store energy in :

1. its electric field
2. its coil
3. its magnetic field
4. both electric and magnetic fields

Q. A transformer is a device which converts:

1. Low voltage at low current into high voltage at high current
2. High voltage at low current into low voltage at high current
3. High voltage at high current into low voltage at low current
4. Electrical power into mechanical power

Q. In a step-down transformer, the number of turns in

1. primary are less.
2. primary are more.
3. primary and secondary are equal.
4. secondary are infinite.

Q. The rms value of current $I_{rms}$ is
(where, $I_0$ is the value of peak current)

1. $\frac{I_0}{2\pi }$
2. $\frac{I_0}{\sqrt{2}}$
3. $\frac{2I_0}{\pi }$
4. $\sqrt{2}{I}_0$

Q. A lamp is connected in series with a capacitor and an AC source. What happens if the capacity of the capacitor is reduced?

1. Brightness may increase or decrease depending on the frequency of the AC
2. There is no change in the brightness of the lamp
3. The lamp shines more brightly
4. The lamp shines less brigthly

Q. In AC circuits choke is preferred to resistors because

1. energy is not wasted.
2. voltage increase.
3. choke coil is cheap.
4. current increases.

Q. If the inductance and capacitance are both doubled in L-C-R circuit, the resonant frequency of the circuit will :

1. Decrease to one-half of the original value
2. Decrease to one-fourth of the original value
3. Decrease to twice the original value
4. Increase to twice the original value

Q. Electromagnetic waves of wavelength ranging from $100\stackrel{\circ }{A}$ to $400\stackrel{\circ }{A}$ comes under :

1. X-rahs
2. UV region
3. Visible region
4. Infrared region

Q. The back emf in a DC motor is maximum when

1. the motor has picked up maximum speed.
2. the motor has just started moving.
3. the motor has just been switched off.
4. the speed of motor is still on increase.

Q. If the power factor in a circuit is unity, then the impedance of the circuit is

1. Inductive
2. Capacitive
3. Partially inductive and partially capacitive
4. Resistive

Q. AC measuring instrument measures

1. rms value
2. any value
3. average value
4. peak value

Q. Inductive reactance of a coil is expressed in

1. Amphere
2. Ohm
3. Weber
4. Volt

Q. One complete set of negative and positive values of alternating quantities is called

1. Amplitude
2. Time period
3. Frequency
4. Cycle

Q. A transformer works on

1. AC only
2. DC only
3. Both AC and DC
4. High voltage only

Q. The frequency of AC mains in India is

1. $110C{s}^{-1}$
2. $50C{s}^{-1}$
3. $60C{s}^{-1}$
4. $120C{s}^{-1}$

Q. The instantaneous value of an AC is given by $I=5sin(\omega t+\varphi )amp$. The rms value of current is

1. $5A$
2. $\frac{5}{\sqrt{2}}A$
3. $5\sqrt{2}A$
4. $2.5A$

Q. Electromagnetic theory suggests that the light consists of:

1. Magnetic vector only
2. Electric vector only
3. Electric and magnetic vectors perpendicular to each other
4. Parallel electric and magnetic vector

Q. The average value of alternating current over complete cycle is

1. Zero
2. $1rms$
3. $\frac{I}{\sqrt{2}}$
4. $2I$

Q. Alternating voltage

1. is independent of time.
2. varies directly with time.
3. varies inversely with time.
4. varies sinusoidaly with time.

Q. A choke coil is used as resistance in

1. AC circuits
2. Half wave rectifier circuits
3. DC circuits
4. Both in AC and DC circuits

Q. In a purely inductive circuit, the current:

1. is in phase with the voltage
2. is out of phase with the voltage
3. leads the voltage by $\pi /2$
4. lags behind the voltage by $\pi /2$