Electricity

Question 1

What is the definition of emf?

Answer 1

EMF is the energy supplied by the cell to each coulomb of charge

Question 2

What is the definition of current ?

Answer 2

Current is the number of coulombs of charge passing a point in 1 second

Question 3

What is the definition of capacitance?

Answer 3

Capacitance is the amount of charge stored per volt.

Question 4

What is a.c.?

Answer 4

a.c. is alternating current - direction of current is continuously changing.

Question 5

What is d.c.?

Answer 5

d.c. is direct current - current flows in one direction only, negative to positive.

Question 6

What is the definition of potential difference?

Answer 6

Potential difference is the number of joules of energy transferred per coulomb of charge.

Question 7

What is the unit for capacitance (C)?

Answer 7

farads F

Question 8

What is the unit for charge (Q)?

Answer 8

coulombs C

Question 9

What is the unit for potential difference (V)?

Answer 9

volts V

Question 10

How would you calculate the peak voltage of the signal shown on the oscilloscope screen?

Answer 10

Measure distance from centre line to top of wave (peak), and multiply this by the number of volts per division

Question 11

What is the definition of r.m.s. voltage (V_rms)?

Answer 11

The r.m.s. voltage (V_rms), or the root mean square voltage, is the value of an a.c. voltage which will deliver the same amount of energy as a d.c. voltage

Question 12

What is meant by an ‘open circuit’?

Answer 12

An open circuit is one in which a current is not flowing (e.g. when a switch is open).

Question 13

What is meant by a ‘short circuit’?

Answer 13

A short circuit is one in which there is no external resistance.

Question 14

From the graph shown, how would the emf be obtained?

Answer 14

The emf is the intercept on the y-axis (the potential difference axis).

Question 15

From the graph shown, how would the internal resistance be obtained?

Answer 15

The internal resistance is equal to the negative of the gradient of the graph.

Question 16

From the graph shown, how would the short-circuit current be obtained?

Answer 16

The short-circuit current is the intercept on the x-axis (the current axis).

Question 17

What does the graph of voltage vs. time look like for charging a capacitor?

Answer 17

Question 18

What does the graph of current vs. time look like for charging a capacitor?

Answer 18

Question 19

What does the graph of voltage vs. time look like for discharging a capacitor?

Answer 19

Question 20

What does the graph of current vs. time look like for discharging a capacitor?

Answer 20

Question 21

What factors affect the time taken for a capacitor to charge (or discharge)?

Answer 21

The time taken for a capacitor to charge (or discharge) depends on the resistance in the circuit and the capacitance of the capacitor.

Question 22

What material does this energy diagram refer to?

Answer 22

Conductor

Question 23

What material does this energy diagram refer to?

Answer 23

Insulator

Question 24

What material does this energy diagram refer to?

Answer 24

Semiconductor

Question 25

What are the majority charge carriers in n-type semiconductor material?

Answer 25

The majority charge carriers in n-type semiconductor material are electrons.

Question 26

In semiconductors, what is meant by the term doping?

Answer 26

In semiconductors, doping is the addition of small amounts of impurity atoms that have either more or fewer valence electrons than the semiconductor.

Question 27

Pure semiconductors can be made to conduct. Explain how this happens.

Answer 27

Pure semiconductors can be made to conduct by increasing their temperature. This makes some electrons gain sufficient energy to move up from the valence band to the conduction band, where they are free to move.

Question 28

Semiconductor materials can be used to produce a voltage when light is incident on the surface of the material. What name is given to this application of the semiconductor?

Answer 28

Using semiconductor material to produce a voltage when light is incident on the surface is known as photovoltaic mode.

Question 29

In a p-n junction, what is meant by forward bias?

Answer 29

Forward bias is when the negative terminal of a cell is connected to the n-type material and the positive terminal of the cell to the p-type material. When connected in this way the p-n junction will conduct.

Question 30

In a p-n junction, what is meant by reverse bias?

Answer 30

Reverse bias is when the positive terminal of a cell is connected to the n-type material and the negative terminal of the cell to the p-type material. When connected in this way the p-n junction will not conduct.

Question 31

In a sample of silicon, impurity Arsenic atoms are added to the structure. Arsenic atoms have 5 outer electrons in their outer shell. What type of semiconductor material does this produce?

Answer 31

In a sample of silicon, impurity Arsenic atoms are added to the structure. Arsenic atoms have 5 outer electrons in their outer shell. This produces n-type semiconductor material.

Question 32

In a sample of silicon, impurity Indium atoms are added to the structure. Indium atoms have 3 outer electrons in their outer shell. What type of semiconductor material does this produce?

Answer 32

In a sample of silicon, impurity Indium atoms are added to the structure. Indium atoms have 3 outer electrons in their outer shell. This produces p-type semiconductor material.