Capacitance (23)

Question 1

State two functions of capacitors in electric circuits

Answer 1

• Storing electrical energy
• Smoothing circuits/voltage levels

Question 2

State the functions of capacitors connected in series and in parallel

Answer 2

IN SERIES:
- Reduce total capacitance, but voltage across each capacitor is the same
- Used for increasing the voltage rating of the circuit
IN PARALLEL:
- Increase total capacitance, but voltage across each capacitor is the same
- Used for increasing the total capacitance of the circuit

Question 3

How are values of Capacitance combined when in series?

Answer 3

1/Ctot = 1/C1 + 1/C2 + 1/C3 ….

Question 4

How are values of Capacitance combined when in parallel?

Answer 4

Ctot = C1 + C2 + C3

Question 5

What is Capacitance?

In isolated spherical conductors

Answer 5

The ratio of charge to potential for a conductor

Question 6

What is Capacitance?

In parallel plate capacitors

Answer 6

• the charge stored on one plate per unit potential difference between the plates

Question 7

How can you find the electrical potential energy stored in a capacitor

Answer 7

• The area under a potential-charge graph
• E= 1/2𝑄𝑉 = 1/2 𝐶𝑉^2

Question 8

When a capacitor discharges through a resistor, what happens to p.d., Q and I

Answer 8

• They all exponentially decrease

Question 9

Why do capacitors store energy and not charge?

Answer 9

• The charges stored on both plates are equal in magnitude and opposite in polarity
• Hence, there is no resultant charge, and it is not stored
• Energy is stored because there is a charge seperation between plates due to the work done by the power supply

Question 10

Explain the mechanism in charging Capacitors

Answer 10

• When the switch is closed, the electrons flow to one of the plates of the capacitor
• This causes electrons to leave the other plate, causing it to be positively charged
• This continues until the p.d. across plates is equal to the Voltage of the power supply