Module 6: Particles and Medical Physics

Question 1

Define capacitance.

Answer 1

The amount of charge a capacitor can store per unit voltage.

Question 2

Define the Farad.

Answer 2

Coulomb per volt.

Question 3

Describe a Q against V graph

Answer 3

Gradient - Capacitance
Area under the graph - Energy stored

Question 4

What is the time constant, τ, of a capacitor

Answer 4

• The time taken for V, I, or Q to decrease to ≅37% when discharging
• τ = RC, where R is the equivalent resistance of the circuit and C is the equivalent capacitance of the circuit.

Question 5

What are some uses of capacitors?

Answer 5

• Camera flash
• Touchscreen
• Back up energy supplies
• When AC is converted to DC, it smoothes the current, ideally τ > > T, where T is the period of the alternating current