Tutorial #5 — AC Basics
Course: FAD1022 Basic Physics 2
Semester: 2 2025/2026
Week: Week #6 (2nd - 6th February 2026)
Centre: Centre for Foundation Studies in Science, Universiti Malaya
Question 1
A voltage divider circuit is connected to a Wheatstone bridge network via a switch (Figure 1).
Determine the:
a) output voltage at Point A relative to the negative terminal of the power supply when the switch is open. b) value of the unknown resistance, $R_{unknown}$ when the switch is closed and the bridge is brought to equilibrium when variable resistor is 3.0 Ohms. c) new output voltage at Point A, relative to the negative terminal of the power supply when the switch is closed and bridge is balanced.
Question 2
The current in an AC circuit is given by:
$$I(t) = 12 \sin(100\pi t)$$
Determine the:
a) peak current b) RMS current c) current when $t = 5 \text{ ms}$ d) frequency and period of the current
Question 3
An AC power supply delivers an RMS current of 5 A at a frequency of 50 Hz to a resistor of $8 \Omega$.
Calculate:
a) The peak current. b) Determine the peak voltage across the resistor. c. Write the expression for the instantaneous voltage.
Question 4
Phasor diagrams below represent two signals at time $t=0$. Sketch the corresponding sinusoidal waveforms for each phasor diagram.
a) V leads I by $\phi = \frac{\pi}{2}$ b) I leads V by $\phi = \frac{\pi}{2}$ c) I leads V by $\phi = \frac{\pi}{4}$ d) V and I in phase
Question 5
The alternating current and voltage in a circuit are given by:
$$I(t) = 4 \cos \omega t$$
$$V(t) = 10 \sin \omega t$$
Determine:
a) The phase difference between the current and voltage. b) State clearly which quantity leads and which lags. c. Draw the phasor diagram showing the correct phase relationship between current and voltage.
Related Concepts
- AC Circuits
- AC Circuit
- Alternating Current
- RMS Value
- Peak Value
- Phasor
- Phase Difference
- Wheatstone Bridge
- Voltage Divider
- Frequency
- Period