Capacitors

Question 1

What is the unit of capacitance?

Answer 1

Farad

Question 2

What is the equation for relative permittivity?

Answer 2

ϵ_r = ϵ_1/ϵ_0 where ϵ_r is relative permittivity, ϵ_1 is the permittivity of the material and ϵ_0 is the permittivity of free space.

Question 3

What is the unit of permittivity?

Answer 3

Fm^-1

Question 4

How do you discharge a capacitor is a circuit with a switch?

Answer 4

Remove the power supply and close the switch then wait for it to discharge.

Question 5

Which equation must be used to find the potential difference between the plates?

Answer 5

Capacitor charging equation (given) but replace the Q’s with V’s.

Question 6

Which equation must be used to find the charging current?

Answer 6

Decay of charge equation (given) but replace the Q’s with I’s.

Question 7

How do you find the time constant from a graph of ln(Q) against t?

Answer 7

Take the negative reciprocal of the gradient.

Question 8

What is the equation for time to halve?

Answer 8

T_1/2 = ln(2)RC

Question 9

What is the equation for time constant given the time to halve?

Answer 9

(T_1/2) / ln(2)