core 3 - p3 Flashcards
(18 cards)
What three functions does a multimeter combine?
Voltmeter, ammeter, and ohmmeter.
Why must a multimeter’s input impedance be very high when measuring voltage?
To avoid loading the circuit and altering measurements.
What is the typical input impedance of a digital multimeter?
10 MΩ or higher (up to >10 GΩ for high-end models)
What is parallax error in analog meters, and how is it minimized?
Misreading due to viewing angle; minimized using mirrored scales.
Name two advantages of digital multimeters over analog ones.
Higher accuracy, no parallax error, automatic calibration.
What does a “half-digit” mean in a digital multimeter?
The first digit can only display 0 or 1 (e.g., a 4½-digit meter shows up to 19999).
Define DC and give an example of a DC source
Unidirectional current flow; example: battery.
Why is DC used in applications like railways and aluminum smelting?
Efficient for long-distance power transmission and electrochemical processes.
What is the standard AC frequency in most countries
50 Hz or 60 Hz (e.g., 50 Hz in the UK, 60 Hz in the USA).
Write the equation for a sinusoidal AC voltage waveform.
v(t)=Vm sin(ωt), where ω=2πf.
Calculate the RMS voltage if V peak = 325V.
V rms = 325/√ 2 ≈ 230V.
What is the form factor for a sine wave?
1.11 (ratio of RMS to average voltage).
How is a sine wave represented in a phasor diagram?
As a rotating vector with magnitude Vm and angular velocity ω.
In a purely inductive AC circuit, how does current relate to voltage?
Current lags voltage by 90°.
In a purely capacitive AC circuit, how does current relate to voltage?
Current leads voltage by 90°.
Define impedance (Z) and its unit
Total opposition to AC current (resistance + reactance). Unit: Ohm(Ω).
What is “true power” in an AC circuit?
Power dissipated in resistance: P=(I ^ 2) R.
How is power factor defined ?
cosθ, where θ is the phase angle between voltage and current.
