6.1: Capacitors, F

Question 1

Define: Capacitor

Answer 1

An electrical component that stores charge by separating them into two electrical conductors with an insulator in between them

Question 2

Define: Capacitance

Answer 2

Amount of charge per unit voltage

Question 3

What is 1 Farads equivalent to?

Answer 3

1 Coulomb per volt (C=Q/V)

Question 4

What happens to the potential difference(p.d.) when you put multiple capacitors in a parallel circuit?

Answer 4

The p.d. of each capacitor is the same

Same as p.d. across resistors in parallel

Question 5

What happens to the p.d. when you put multiple capacitors in a series circuit?

Answer 5

The p.d. of each capacitor is shared between them

similar to p.d. across resistors in series

Question 6

The total capacitance for a ________ circuit is:

C total = C1 +C2 + ……

Answer 6

Parallel circuit

Question 7

The total capacitance for a ______ circuit is:

1/Total = 1/C1 + 1/C2 + ……

Answer 7

Series circuit

Question 8

What simple maths equation can you use to derive:

W = 1/2QV

Answer 8

Area of triangle = 1/2 x base x height

∴ the area under a graph is energy stored

Question 9

Name an advantage and disadvantage of using a capacitor over a battery

Answer 9

Advantage: Can discharge quicker than batteries (and/or) amount of charge can be stored and released at a chosen rate.
Disadvantage: Can’t store as much charge

Question 10

Give 3 different uses of capacitors

Answer 10

• Flash photography
• Back-up power supplies
• Smoothing out p.d. (When converting from A.C. to D.C)

Question 11

The charge on a discharging capacitor decreases _____________

Answer 11

The charge on a discharging capacitor decreases exponentially

Question 12

As a capacitor discharges what other two variables decrease exponentially.

Answer 12

Potential difference and current

Similar equation to discharging

Question 13

How is discharging a capacitor similar to radioactive decay?

Answer 13

Always takes the same amount of time for the charge to halve, regardless of the amount of charge you started with

Question 14

What 2 factors does does time taken to charge or discharge rely on?

Answer 14

• Capacitance of the capacitor (affects amount of charge which is transferable at a given voltage)
• Resistance of circuit (affects current in circuit)

Question 15

Define: time constant (t = CR) in terms of a discharging capacitor

Answer 15

Time taken for the charge,p.d. or current on a discharging capacitor to fall to 37% of it’s initial value

Question 16

Define: time constant (t = CR) in terms of a charging capacitor

Answer 16

Time taken for the charge,p.d. or current of a charging capacitor ro rise to 63% of its maximum value

Question 17

What effect does resistance have on a capacitor (in series)

Answer 17

The larger the resistor, the longer it takes to charge or discharge

Question 18

In practice what is the time taken for a capacitor to fully discharge or charge

Answer 18

Roughly 5 CR(time constants)