CCEA A-Level Physics 1210
Physical Quantities, Scalars and Vectors
Moments and Equilibrium
Linear Motion and Dynamics
Newton's Laws of Motion
Linear Momentum and Impulse
Work, Energy and Power
Current, Charge and Potential Difference
Resistance and Resistivity
Internal Resistance and Potential Dividers
Waves
Refraction
Lenses
Superposition, Interference and Diffraction
Quantum Physics
Wave-Particle Duality
Astronomy
Practical Skills and Data Analysis
Deformation of Solids
Thermal Physics
Uniform Circular Motion
Simple Harmonic Motion
The Nucleus and Radioactive Decay
Nuclear Energy, Fission and Fusion
Gravitational Fields
Electric Fields
Capacitors
Magnetic Fields
Charged Particles and Accelerators
Capacitors
Uses of capacitors in circuits
- 3 things to know
- Unit A2 2
Overview
Effect of using too small a smoothing capacitor, working voltage of a capacitor and how it depends on the plate separation.
What you need to know
Answer each one before you reveal it.
What decides how well a smoothing capacitor works?
What is the effect of using too small a smoothing capacitor?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Why does a capacitor block direct current but pass alternating current?
Model answer
A steady voltage charges it once and then no more charge flows, whereas an alternating voltage keeps charging and discharging it so current continues in the circuit.
- 2
How is a capacitor used to smooth a rectified supply?
Model answer
It is connected across the output and charges at the peaks and discharges between them, so the voltage falls much less between one peak and the next.
- 3
What decides how well a smoothing capacitor works?
Model answer
The time constant of the capacitor with the load, which must be long compared with the time between peaks.
- 4
What is the effect of using too small a smoothing capacitor?
Model answer
The capacitor discharges substantially between peaks, so a large ripple voltage remains on the output.
- 5
How is a capacitor used in a timing circuit?
Model answer
It charges through a resistor and the circuit switches when the potential difference reaches a set value, so the delay is set by the time constant.
- 6
A timing circuit must give a delay of about 5 s using a 100 kΩ resistor. Suggest a suitable capacitance.
Model answer
C = τ/R = 5 ÷ 100 × 10³, which is 5 × 10⁻⁵ F, so a 47 μF capacitor is a suitable standard value.
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