Electricity: 3 - Capacitators

Question 1

What does a typical capacitor consist of?

Answer 1

Two conducting layers separated by an insulator like air.

Question 2

What is the circuit symbol for a capacitor?

Answer 2

• | |-

Question 3

What does a larger capacitance mean for a capacitor?

Answer 3

The larger the capacitance the more energy it can store and the longer it takes to charge.

Question 4

What is the symbol for capacitance?

Answer 4

C

Question 5

What are the units for capacitance?

Answer 5

Farads, F.

Question 6

What will a capacitor of 1 farad store?

Answer 6

A capacitor of 1 farad will store 1 coulomb of charge when the potential difference across it is 1 volt.

Question 7

What is a device that is to store charge called?

Answer 7

A capacitor.

Question 8

What is capacitance known as?

Answer 8

The ability of a component to store charge.

Question 9

What are the prefixes normally associated with farads and why is this?

Answer 9

Micro farads (μF)= 1x10-6 and nano farads (nF)= 1x10-9 as the farad is too large a unit for practical purposes.

Question 10

What is the equation for capacitance using charge?

Answer 10

C=Q/V

Question 11

In a resistive circuit what is the current and how is this shown on a graph?

Answer 11

In a resistive circuit the current is independent of a.c. frequency. On a graph of frequency against current the current is just a straight line.

Question 12

In a capacitive circuit what is the circuit and how is this shown on the graph?

Answer 12

For a capacitive circuit, current increases as frequency increases. On a graph looks like a diagonal line across the graph which does not touch the axes.

Question 13

What does a voltage charging capacitor graph against time look like?

Answer 13

A curved/hump line that curves outwards and goes through the origin.

Question 14

What does a voltage discharging capacitor graph against time look like?

Answer 14

A line that curves down inwards and reaches the voltage of 0 and looks like a mountain drop.

Question 15

What does a current charging capacitor graph against time look like?

Answer 15

A line that curves down wards like that of the voltage discharging and starts high with a high current the goes low but does not touch the axis.

Question 16

What does a current discharging capacitor graph against time look like?

Answer 16

A line that curves upwards like a hump and similar to the voltage charging. Starts at minus and increases nearer to 0 but does not touch any of the axis.

Question 17

What is the total energy stored in a capacitor equal to?

Answer 17

The area under the graph of charge against potential difference.

Question 18

What is the equation to calculate the energy stored in a capacitor using the area under a charge against potential difference graph?

Answer 18

E=1/2 QV

Question 19

What is the equation for the energy stored in a capacitor using capacitance and voltage and how is this formed?

Answer 19

E=1/2 QV
E=1/2 (CV)V
E=1/2 CV²

Question 20

What is the equation for the energy stored in a capacitor using capacitance and charge and how is this formed?

Answer 20

E= 1/2 QV
E= 1/2 Q(Q/C)
E= 1Q ²/2C

Question 21

What can be done to increase the time that it takes to charge a capacitor?

Answer 21

Increase the resistance in the circuit or increase the capacitance of the resistor.

Question 22

What are uses of capacitors?

Answer 22

Blocking capacitor like in an oscilloscope, camera flash, touch screen phones and smoothing.

Question 23

How does the capacitor work in a camera flash?

Answer 23

A camera flash requires a rapid release of energy. A battery can be used to charge a capacitor, the capacitor can then provide a very high current which produces a bright flash.