Alternating Current

In a series L-C-R circuit, resistance R = 10 Ω and the impedance Z = 10 Ω. The phase difference between the current and the voltage is

• 0^o

• 30^o

• 45^o

• 60^o

The impedance of a circuit, when a resistance R and an inductor of inductance L are connected in series in an AC circuit of frequency f, is

• $\sqrt{\mathrm{R} + 2 {\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

• $\sqrt{\mathrm{R} + 4{\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

• $\sqrt{{\mathrm{R}}^2 + 4 {\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

• $\sqrt{{\mathrm{R}}^2 + 2{\mathrm{\pi }}^2 {\mathrm{f}}^2 {\mathrm{L}}^2}$

A choke is preferred to a resistance for limiting current in AC circuit because

• choke is cheap

• there is no wastage of power

• choke is compact in size

• choke is a good absorber of heat

Induced emf in the coil depends upon

• conductivity of coil

• amount of flux

• rate of change of linked flux

• resistance of coil

In an L-C-R circuit inductance is changed from L to L/2.To keep the same resonance frequency, C should be changed to

• 2 C

• $\frac{\mathrm{C}}{2}$

• 4 C

• $\frac{\mathrm{C}}{4}$

220 V, 50 Hz, AC source is connected to an inductance of 0.2 Hand a resistance of 20 Ω in series. Whatis the current in the circuit?

• 3.33 A

• 33.3 A

• 5 A

• 10 A

If we change the value of R, then

• voltage does not change on L

• voltage does not change on LC combination

• voltage does not change on C

• voltage changes on LC combination

Real power consumption in a circuit is least when it contains.

• high R, low L

• high R, high L

• low R, high L

• high R, low C

The rms speed (in m/s) of oxygen molecules of the gas at temperature 300 K, is

• 483

• 504

• 377

• 346

An inductor (L = 20 H), a resistor (R = 100 Ω) and a battery (E = 10 V) are connected in series. After a long time, the circuit is short-circuited and then the battery is disconnected. Find the current in the circuit at 1 ms after short circuiting.

• 4.5 x 10⁵ A

• 3.2x 10^-5 A

• 9.8 × 10^-5 A

• 6.7 × 10^-4 A