Capacitance

Question 1

Define capacitance.

Answer 1

The charge per volt stored in a capacitor.

Question 2

How do you calculate capacitance?

Answer 2

C = Q / V

Question 3

How do you calculate energy stored in a capacitor?

Answer 3

E = 1/2(QV)

E = 1/2(V²C)
E = 1/2(Q²/C)

Question 4

When charging a capacitor which way does the current flow?

Answer 4

Away from the negative terminal of the cell and towards the positive terminal. Opposite to conventional current.

Question 5

When discharging a capacitor which way does current flow?

Answer 5

Away from the positive terminal and towards the negative terminal. Conventional current.

Question 6

Why does the rate of change of pd decrease as a capacitor discharges?

Answer 6

Current decreases.
Charge lost slower so pd is lost slower as V∝Q.

Question 7

What is a dielectric? (Capacitors)

Answer 7

An insulating material with a relative permeability that allows for more charge to be stored in a capacitor.

Question 8

How does a dielectric material increase charge in a capacitor?

Answer 8

The dielectric molecules between the charged plates become polarised.

These molecules align themselves positive to negative and vice versa.

This increases the force of attraction/repulsion so more electrons are attracted to the positive plate and repelled from the negative plate.

Question 9

How do you calculate the relative permeability of a dielectric?

Answer 9

εᵣ = Q/Q₀