In an AC circuit, the emf (e) and the current (i) at any instant are given respectively by
e = E0 sin ωt
i = Io sin (ωt -Φ)
The average power in the circuit over one cycle of AC is
C.
The power is defined as the rate at which work is being done in the circuit.
Power = rate of work done in one complete cycle.
Or
Pav = W/T
where cos Φ is called the power factor of an AC circuit.
A charged particle (charge q ) is moving n a circle of radius R with uniform speed v. The associated magnetic moment μ is given by:
qvR/2
qVR2
qVR2/2
qVR2/2
A.
qvR/2
As revolving charge is equivalent to a current so
I = qf = q x ω/ 2π
But ω = v/R
Where R is radius of circle and v is uniform speed of charged particle, therefore,
I= qv/2πR
Now, magnetic moment associated with charged particle is given by
μ = IA = I x πR2
μ = qv/2 πR2
= qvR/2
The primary and secondary coil of a transformer have 50 and 1500 turns respectively. If the magnetic flux Φ linked with the primary coil is given Φ = Φo +4t, where Φ is in weber, t is time is second and Φo is a constant the output voltage across the secondary coil is:
90 V
120 V
220 V
220 V
B.
120 V
The magentic flux linked with the primary coil is given by
Φ = Φo +4t
So, voltage across primary
Vp = dΦ/dt = d(Φ+dt) /dt
= 4 volt (Φ = constant)
Also, we have
Np = 50 and Ns = 1500
From relation ,
Vs/Vp = Ns/Np
Vs = 4 x (1500/50)
= 120 V
A common emitter amplifier has a voltage gain of 50, an input impedance of 100 Ω and an output impedance of 200 Ω. The power gain of the amplifier is:
500
1000
1250
1250
C.
1250
AC power gain is ratio of change in output power to the change in input power.
AC power gain
In the circuit shown, the current through the 4 Ω resistor is 1 A when the points P and M are connected to a DC voltage source. The potential difference between the point M and N is 
1.5 V
1.0 V
0.5 V
0.5 V
D.
0.5 V
In parallel resistances, the potential difference across them is same.
Potential difference across PM
V = 4 x 1 = 4 Volt (ie, across 4 Ω)
Equivalent resistance of lower side arm, 
Now the circuit can be shown as
Let current I flow in lower branch, so
1.25 I = 4V
I = 4/1.25 = 3.2 A
Therefore, 3.2 A current flows in 1 Ω resistance, hence potential difference between M and N is
V' = 3.2 x 1 = 3.2 volt
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