Online Test — Electromagnetic Induction and Alternating Current
20 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 20
The SI unit of magnetic flux is the:
tesla
weber
henry
farad
Explanation: $1\,\text{Wb} = 1\,\text{T}\cdot\text{m}^2$.
Question 2 of 20
Magnetic flux $\Phi = BA\cos\theta$ is zero when the field is:
perpendicular to the plane
in the plane of the surface
at 60°
very strong
Explanation: If the field lies in the plane, $\theta = 90^\circ$ and $\cos 90^\circ = 0$.
Question 3 of 20
Faraday's law states that the induced EMF equals:
the flux
the rate of change of flux
the current
the resistance
Explanation: $\varepsilon = -N\,d\Phi/dt$.
Question 4 of 20
The negative sign in Faraday's law represents:
Ohm's law
Lenz's law
Coulomb's law
Gauss's law
Explanation: It shows the induced current opposes the change in flux (Lenz's law).
Question 5 of 20
Lenz's law is based on the conservation of:
charge
energy
momentum
mass
Explanation: The opposing induced current ensures energy is conserved.
Question 6 of 20
Motional EMF of a rod is given by:
$Bl/v$
$Blv$
$Bv/l$
$v/Bl$
Explanation: $\varepsilon = Blv$ for a rod moving perpendicular to the field.
Question 7 of 20
Eddy currents are reduced in a transformer core by:
thicker core
lamination
more current
using copper core
Explanation: Laminations break up eddy-current loops.
Question 8 of 20
The SI unit of self-inductance is the:
weber
henry
tesla
ohm
Explanation: $L$ is measured in henry (H).
Question 9 of 20
The RMS value of an AC current is:
$I_0$
$I_0/\sqrt2$
$I_0\sqrt2$
$2I_0$
Explanation: $I_{rms} = I_0/\sqrt2 \approx 0.707\,I_0$.
Question 10 of 20
In a pure inductor, the current:
leads voltage by 90°
lags voltage by 90°
is in phase
is zero
Explanation: Current lags voltage by a quarter cycle in an inductor.
Question 11 of 20
Inductive reactance $X_L$ equals:
$1/\omega L$
$\omega L$
$\omega C$
$L/\omega$
Explanation: $X_L = \omega L$ rises with frequency.
Question 12 of 20
Capacitive reactance $X_C$ equals:
$\omega C$
$1/\omega C$
$\omega L$
$C/\omega$
Explanation: $X_C = 1/\omega C$ falls with frequency.
Question 13 of 20
The impedance of a series LCR circuit is:
$R + X_L + X_C$
$\sqrt{R^2 + (X_L - X_C)^2}$
$R - X_L - X_C$
$RX_LX_C$
Explanation: $Z = \sqrt{R^2 + (X_L - X_C)^2}$.
Question 14 of 20
At series resonance, the impedance equals:
zero
R
$X_L$
infinity
Explanation: $X_L = X_C$ cancel, so $Z = R$ (minimum).
Question 15 of 20
The resonant angular frequency of an LCR circuit is:
$\sqrt{LC}$
$1/\sqrt{LC}$
$2\pi LC$
$LC$
Explanation: $\omega_0 = 1/\sqrt{LC}$.
Question 16 of 20
Average power in an AC circuit is:
$V_{rms}I_{rms}$
$V_{rms}I_{rms}\cos\phi$
$V_0I_0$
$I^2_{rms}X_L$
Explanation: $P = V_{rms}I_{rms}\cos\phi$, where $\cos\phi$ is the power factor.
Question 17 of 20
For a transformer, $V_s/V_p$ equals:
$N_p/N_s$
$N_s/N_p$
$I_s/I_p$
$1$
Explanation: $V_s/V_p = N_s/N_p$.
Question 18 of 20
A transformer operates only on:
DC
AC
both
neither
Explanation: Mutual induction needs the changing flux that AC provides.
Question 19 of 20
The frequency of LC oscillations is:
$2\pi\sqrt{LC}$
$1/(2\pi\sqrt{LC})$
$1/\sqrt{LC}$
$\sqrt{LC}$
Explanation: $f = 1/(2\pi\sqrt{LC})$.
Question 20 of 20
The power factor of a pure resistor is:
0
1
0.5
0.707
Explanation: Voltage and current are in phase, so $\cos 0^\circ = 1$.