Paper 1 Alternating Current Drills

Q1

An alternating current is one that

A. has constant magnitude and direction.
B. changes direction periodically.
C. is always zero mean power.
D. cannot heat a resistor.

Q2

For $V=V_0\sin \omega t$, the peak voltage is

A. $V_0$.
B. $\omega$.
C. $V_0/\sqrt{2}$ only.
D. $2\pi /\omega$.

Q3

Rms voltage is useful because it gives

A. same heating effect as equivalent dc voltage.
B. peak field direction.
C. frequency only.
D. zero average current.

Q4

For a sinusoidal voltage, $V_{\mathrm{rms}}=$

A. $V_0/\sqrt{2}$.
B. $\sqrt{2}{V}_0$.
C. $V_0/2$.
D. $2V_0$.

Q5

Frequency and period are related by

A. $f=1/T$.
B. $f=T$.
C. $f=2\pi T$.
D. $f=T^2$.

Q6

Angular frequency is

A. $\omega =2\pi f$.
B. $\omega =f/2\pi$.
C. $\omega =1/f^2$.
D. $\omega =V/I$.

Q7

Mean value of a complete sinusoidal current over one cycle is

A. zero.
B. peak value.
C. rms value.
D. twice peak.

Q8

Mean power in a resistor supplied by sinusoidal rms values is

A. $P=V_{\mathrm{rms}}{I}_{\mathrm{rms}}$.
B. $P=V_0{I}_0$ always.
C. $P=0$ always.
D. $P=I/V$.

Q9

For a resistor in ac, current and voltage are

A. in phase.
B. $90^{\circ }$ out of phase.
C. always opposite.
D. unrelated.

Q10

The average of ${\sin }^2$ over a cycle is

A. $1/2$.
B. $0$.
C. $1$.
D. $\sqrt{2}$.

Q11

Peak-to-peak voltage for peak $V_0$ is

A. $2V_0$.
B. $V_0/2$.
C. $V_0/\sqrt{2}$.
D. $V_0$.

Q12

Half-wave rectification produces an output that is

A. unidirectional but pulsating.
B. steady dc immediately.
C. unchanged ac.
D. zero always.

Q13

Full-wave rectification uses

A. both half-cycles in same output direction.
B. only positive half-cycles and discards negative.
C. no diodes.
D. only transformers.

Q14

A capacitor smoother across a load reduces

A. ripple.
B. frequency to zero always.
C. rms value to zero.
D. resistance.

Q15

In $V=12\sin (100\pi t)$, frequency is

A. $50\mathrm{Hz}$.
B. $100\mathrm{Hz}$.
C. $12\mathrm{Hz}$.
D. $100\pi \mathrm{Hz}$.

Q16

A $230\mathrm{V}$ mains value usually refers to

A. peak voltage.
B. rms voltage.
C. peak-to-peak voltage.
D. mean voltage over cycle.

Q17

The rms current through a $10\Omega$ resistor connected to $20{\mathrm{V}}_{\mathrm{rms}}$ is

A. $2.0\mathrm{A}$.
B. $0.50\mathrm{A}$.
C. $200\mathrm{A}$.
D. $20\mathrm{A}$.

Q18

The peak value of $4.0{\mathrm{A}}_{\mathrm{rms}}$ sinusoidal current is

A. $5.66\mathrm{A}$.
B. $2.83\mathrm{A}$.
C. $4.0\mathrm{A}$.
D. $8.0\mathrm{A}$.

Q19

Power loss in a cable is often calculated using

A. $I_{\mathrm{rms}}^{2}R$.
B. $I_{0}R$ only.
C. $V{R}^2$.
D. $Q/V$.

Q20

Rms is found by

A. root of mean of square.
B. mean of root of square only.
C. square of mean.
D. peak minus mean.