Unit 5 Electricity

Question 1

Define electric current

Answer 1

Rate of flow of charge

Question 2

What does an electric current on one amp represent?

Answer 2

Rate of flow of charge of one coulomb per second

Question 3

Define potential difference

Answer 3

Work done per unit charge

Question 4

What is the resistance of a component?

Answer 4

Measure of how much a component opposes the flow of current

Question 5

How can the resistance of an electrical component be found?

Answer 5

Measure the current through it and the potential difference across it

Question 6

State Ohm’s law

Answer 6

Current through a metallic conductor is directly proportional to the potential difference across it, provided the physical conditions of the conductor do not change

Question 7

What is the name for a conductor that obeys Ohm’s law?

Answer 7

Ohmic conductor - constant resistance

Question 8

Describe the I-V characteristic for an ohmic conductor

Answer 8

Straight line graph through the origin

Question 9

Describe the I-V characteristic for a filament lamp

Answer 9

Curve with a decreasing gradient
As more current flows through the filament, the temperature increases. The atoms and ions in the wire vibrate more, and collide more often with the electrons flowing through it so there is more resistance.

Question 10

Describe the I-V characteristic for a diode

Answer 10

With forward bias, graph starts at (0/0) and increases gradually
With reverse bias, graph extends along the potential with almost zero current

Question 11

What is a negative temperature coefficient thermistor?

Answer 11

Component for which the resistance decreases when temperature increases

Question 12

What is a superconductor?

Answer 12

Material with zero resistivity at and below a critical temperature

Question 13

Why are superconductors useful?

Answer 13

Current in a superconductor has no heating effect so no energy is lost

Question 14

State the law of conservation of charge

Answer 14

Charge cannot be created or destroyed, so the amount to charge in a closed systems remains the same

Question 15

State Kirchoff’s first law

Answer 15

Total current leaving any junction in a circuit is equal to the total current entering that junction

Question 16

Define the potential difference between two points in a circuit

Answer 16

Energy transferred per coulomb of charge that flows from one point to the other

Question 17

What is a potential drop in a circuit?

Answer 17

Potential difference between two points in a circuit if the charge carriers lose energy

Question 18

State Kirchoff’s second law

Answer 18

Sum of the e.m.f.s around any loop in a circuit is equal to the sum of the p.d.s around the loop

Question 19

Give the potential difference rule for two or more components in series

Answer 19

Total potential difference across all the components is equal to the sum of the potential differences across each component

Question 20

Give the equation for calculating the total resistance for two or more resistors connected in series.

Answer 20

R(total) = R1 + R2 + R3. + …

Question 21

What can a potential divider circuit do as part of a sensor circuit?

Answer 21

Supply a potential difference that varies with physical conditions, such as temperature or light intensity

Question 22

What is a potentiometer?

Answer 22

Variable potential divider that uses a single variable resistor to allow V(out) to be varied from 0V to the maximum source potential difference

Question 23

Define the electromotive force of a power supply and give its unit

Answer 23

Electrical energy per unit charge produced by the source, in volts

Question 24

What is internal resistance?

Answer 24

The resistance to target flow of current inside the power supply due to the collisions between the electrons in the current and the atoms in the supply

Question 25

Give the equation for calculating the lost potential difference across a power supply’s internal resistance

Answer 25

Lost volts = I x r

Question 26

What is the benefit of connecting cells in parallel?

Answer 26

Providing longer lasting energy supply because the total store of energy is greater