Test: Alternating Current - 2 - CUET Humanities MCQ

When magnetic flux linked with a coil changes, induced emf is produced in it and the induced current flows through the wire forming the coil. In 1895, Focault experimentally found that these induced currents are set up in the conductor in the form of closed loops. These currents look like eddies or whirlpools and likewise are known as eddy currents. They are also known as Focault's currents. These current oppose the cause of their origin. Therefore, due to eddy currents, a great amount of energy is wasted in form of heat energy. To minimise these current, the core of transformer should be laminated.

Z = (R² + X_L²)^1/2
Z = {(40)² + (30)²}^1/2 = 50 ohms
I = V/Z = 200/50 = 4 A

For series LCR circuit, effective voltage is V = 

The resonance frequency of LC circuit is:

C = 8.44 pF

Energy stored in capacitor is equal to energy stored in inducatance.
Here, CV² = LI²
or C = 
= 
= 25 μF

As alternating current is periodic, its value should repeat after fixed interval of time. Therefore, its amplitude has to be constant.

R = P/I²
= 200/4 = 50 ^Ω
Z =  = 
Z = V/I = 220/2  = 110 ohm
X₂^L = 12100 - 2500 = 9600
X_L = 98 ohm
L =  =  =  = 0.312 H

If energy is stored equally in electric and magnetic fields, then energy in electric field will be half of the maximum value, which occurs when the charge on the capacitor is maximum.
Energy in capacitor = 1/2 (Q^2/2c) 

Q' = Q/√2

AC is referred as alternating current because it keeps on reversing its direction.

In the given circuit, When only the capacitance is removed, the current leads the voltage by 60°
So we have
tan60º  = X_C/R ....(1)
When only the inductance is removed, the current leads the voltage by 60°.
tan60º = XL/R ....(2) 
From 1 and 2, we have
X_C = X_L
Hence Impedance of the circuit is

Hence Current can be calculated as
V = IZ = IR ⇒ I = V/R
I = 200/100 = 2A

Alternating current cannot be used in a/an galvanometer . Galvanometer is a device which detects (not measure) the flow of Direct Current (DC) only. This is because the galvanometer's needle moves in a direction according to the direction of current. This is only possible in the case of DC current.

The average value or mean value of alternating current for one complete cycle is zero because half the time current is +ve, while half the time is -ve, and they are in equal proportion. Hence, average current is zero.

Efficiency of a transformer is defined as the ratio of output power to the input power. A transformer which decreases the AC voltage is called a step down transformer. Transformer is essentially an AC device. It cannot work on DC. A transformer changes AC voltage/currents. Efficiency of transformer is given by

Here, P_output = 8 kW, η = 90%
P_input =  kW
= 8.89 kW