10 minutes maximum! (can you do it in 5?)


1. Capacitors are made using 'dielectric materials'. Which of these statements best describes a dielectric material?
 A. A conductor that can be polarised.
 B. A conductor that cannot be polarised.
 C. An insulator that can be polarised.
 D. An insulator that cannot be polarised.


2. 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:
 A. C
 B. 2 C
 C. 4 C
 D. 8 C


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


Charge (C) 
Energy (J) 
A 
10^{3} 
5 x 10^{4}^{} 
B 
10^{5} 
5 x 10^{4}^{} 
C 
10^{3} 
5 x 10^{3}^{} 
D 
10^{5} 
5 x 10^{3}^{} 


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


Series 
Parallel 
A 
3F 
3/2 F^{} 
B 
2/3 F^{} 
3 F 
C 
3 F 
2/3 F 
D 
3/2 F^{} 
3 F 


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



6. 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?
 A. e
 B. e^{1}
 C. 0.5
 D. 0


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



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



9. The energy stored in a capacitor is E when charged to a voltage V_{0}. After a time τ the potential difference across the capacitor has fallen to 0.69 V_{0} as it discharges through a resistor. This means that the energy transferred to the resistor in this time will be:
 A. 0.31^{} E
 B. 0.69^{2} E^{}
 C. (1  0.69^{2}^{}) E
 D. 0.31^{2}^{} E


10. A capacitor discharges through a fixed resistor. The time constant τ for the capacitor and resistor is 10 seconds. At what time will the charge across the capacitor have dropped to half the original value?
 A. 0.5.e^{10}
 B. 10.e^{0.5}
 C. 10.ln(0.5)
 D. 10.ln(0.5)


