Module 6 - Capcitors (Capcitors)

Question 1

Define Capacitance

Answer 1

charge stored per unit potential difference

Question 2

What is a capacitor

Answer 2

2 metalllic plates separated by an insulated, used to separate charge

Question 3

what is the equation for capacitance

Answer 3

C = Q/V
C - capacitance in F (farads)

Question 4

What is the unit farad

Answer 4

A capacitor has a capacitance of 1 F when its plates store 1 coulomb of charge per volt across the plates

Question 5

When initially charging a capacitor what happens on the positive side of the circuit

Answer 5

Electrons on the plate connected to the positive terminal are attracted to it, so they leave the plate and move toward the terminal.

Question 6

When initially charging a capacitor what happens on the negative side of the ciruit

Answer 6

Electrons at the negative terminal are repelled by it, so they leave and deposit on the plate connected to it

Question 7

Describe the 1:1 interaction within the charging of a capacitor

Answer 7

For every electron removed from the positive plate an electron is deposited on the negative plate

Question 8

How does a potential difference form on charging plates

Answer 8

One plate becomes positve and the other negative as electrons flow, creatinfg a uniform electric field between the plates

Question 9

Why does the separation of charge beome harder over time

Answer 9

As charge builds up, the negative plate repels electrons more and the positive plate attracts them more, making further charge separation harder.

Question 10

When has the capacitor stopped charging

Answer 10

When the capacitor’s potential difference equals the emf, the emf can no longer overcome the capacitor’s opposing pd, so charging stops.

Question 11

In the scenario of overcoming the resistance to charge separation during charging a capacitor what does the pd between the plates represent

Answer 11

The work done per unit charge to move from one capacitor plate to the other

Question 12

Why is an insulator used

Answer 12

To stop electrons flowing through the plates

Question 13

What is the value of current in a charged capacitor

Answer 13

0A

Question 14

Explain how a capacitor starts to discharge

Answer 14

A capacitor discharges once the emf source is removed, as only its own potential difference now drives the electrons.

Question 15

State and explain how Q, I, V change as a capacitor charges

Answer 15

Q increases, because more charge is being separated to each plate
I decreases, because separating charge becomes harder so less charge will flow per unit time
V increases because separating charge becomes harder, so more work is done per unit charge to separate it

Question 16

State and explain how Q, I, and V change as a capacitor discharges

Answer 16

Q decreases, as more electrons are released into the circuit and so less charge is separated
I decreases, because over time the potential difference decreases, so the driving force pushing electrons decreases
V decreases, as less charge is separated so the strength of the electric field between the plates decrease

Question 17

What is the equation for capacitance in series

Answer 17

1/C = 1/C1 +1/C2

Question 18

What is the equation for capacitance in parallel

Answer 18

C = C1 + C2 + …