Pre-U Capacitors

Two plates hold identical and opposite electric charges, +Q and -Q, and are separated by a distance d. What is the electric potential at the mid-point between these two plates?

• 2Q

• Q / d

• 2Q / d

• zero

Capacitors are made using 'dielectric materials'. Which of these statements best describes a dielectric material?

• A conductor that can be polarised

• A conductor that cannot be polarised

• An insulator that can be polarised

• An insulator that cannot be polarised

A simple capacitor of capacitance C is produced using 2 parallel plates of area A and separation d. (Air is used as the dielectric material). If the separation of the plates is halved to d/2 and the area of both plates is doubled, the new capacitance will be:

• C

• 2 C

• 4 C

• 8 C

A 10^-4 F capacitor is connected to a 10 V cell. What is the charge and energy stored on the capacitor?

• A

• B

• C

• D

Two large capacitors of value 1 F and 2 F are wired in series and then in parallel. What is the total capacitance when combined like this?

• A

• B

• C

• D

Identical capacitors are connected in different combinations. Which of these capacitor networks has the largest capacitance?

• A

• B

• C

• D

The formula τ = RC can be used to find the time constant for the discharge of a capacitor through a resistor. The capacitor is initially charged to a potential of 1 V.

At a time t = τ, what is the voltage in volts across the capacitor?

• e

• e^-1

• 0.5

• 0

Which of the following graphs best shows the potential difference across a capacitor discharging through a resistor?

• A

• B

• C

• D

Which of the following graphs best shows the potential difference across a capacitor charging through a resistor?

• A

• B

• C

• D

The energy stored in a capacitor is E when charged to a voltage V₀. After a time τ the potential difference across the capacitor has fallen to 0.69 V₀ as it discharges through a resistor. This means that the energy transferred to the resistor in this time will be:

• 0.31 E

• 0.69² E

• (1 - 0.69²) E

• 0.31² E