Unit 5 - Current Electricity

Question 1

What is electric current?

Answer 1

The rate of flow of charge or the amount of charge that flows per second

Question 2

Is the Amp or the Coulomb a base unit?

Answer 2

The Amp is a base unit whilst the Coulomb is a defined unit

Question 3

What is the structure of a materials with metallic bonding?

Answer 3

In a material with metallic bonding there is a rigid structure of vibrating positive ions in a sea of delocalised electrons

Question 4

How do the delocalised electrons in a metal move?

Answer 4

These electrons move randomly and at very high speeds

Question 5

What happens to the movement of electrons when you apply a potential difference to a material?

Answer 5

The electrons do not all move in the same direction, they still move randomly but they have a net movement around the circuit

Question 6

Which direction will the net movement of electrons be in a circuit?

Answer 6

From the negative terminal of the power supply to the positive terminal of the power supply

Question 7

What is electron flow?

Answer 7

The direction which electrons move around a circuit (negative to positive terminal)

Question 8

What is current flow?

Answer 8

The direction from the positive terminal to the negative terminal of the power supply (the opposite direction to electron flow)

Question 9

What is potential difference?

Answer 9

The energy per unit charge given up by charges as they pass through a device

Question 10

What is electromotive force?

Answer 10

The energy per unit charge that is picked up

Question 11

What happens if you add batteries in parallel?

Answer 11

The energy stored in the circuit increases giving it a longer battery life but the same intensity because charges still carry the same amount of charge

Question 12

What happens if you add batteries in series?

Answer 12

The charges pick up more charge so the intensity of the circuit will increase

Question 13

Define Electrical Resistance

Answer 13

A measure of the opposition to the flow of charges through a conductor

Question 14

What is the relationship between resistance and current?

Answer 14

Resistance and current are inversely proportional which means thats as resistance increases current will decrease

Question 15

What is the relationship between resistance and potential difference?

Answer 15

Resistance and potential difference are directly proportional which means that, as resistance increases potential difference will also increase

Question 16

What is Ohm’s Law?

Answer 16

Ohm’s Law states that: “the current through a conductor is directly proportional to the potential difference across it, provided that the conditions do not change”

Question 17

Why will an increase in temperature increase the resistance in a metal conductor?

Answer 17

Metals consist of positively charged ions vibrating about a fixed point in a sea of electrons. These electrons are what travelling around a circuit to create current. Resistance is caused by electrons colliding with the ions and losing their energy. When the temperature increases the electrons are more likely to collide with the ions meaning the resistance increases.

Question 18

Why does a current flowing through a material cause it to heat up?

Answer 18

Temperature if a measure of the mean kinetic energy of particles, when current is flowing electrons are colliding with ions and transferring their energy which causes the temperature to increase

Question 19

What are superconductors?

Answer 19

Superconductors are conductors which have the potential to have no resistance at very low temperature (around -140 C)

Question 20

With regards to the physical properties of a material, which two things is resistance dependent on?

Answer 20

Length and cross sectional area

Question 21

What is the relationship between length and resistance?

Answer 21

As the length increases the resistance increase, the are directly proportional

Question 22

What is the relationship between cross sectional area and resistance?

Answer 22

As the cross sectional area increases the resistance decreases, they are inversely proportional

Question 23

What is resistivity?

Answer 23

Resistivity is a constant property of a material at a certain temperature, it is the constant that arises from combing the directly proportional equation between length and resistance and the equation for inverse proportion between cross sectional area and resistance

Question 24

What happens when you add a resistor in series?

Answer 24

The resistance increases

Question 25

What happens when you add a resistor in parallel?

Answer 25

The resistance decreases

Question 26

What is the equation for resistors in series?

Answer 26

RTotal = R1 + R2 + R3 …

Question 27

What is the equation for resistors in parallel?

Answer 27

1/RTotal = 1/R1 + 1/R2 + 1/R3 …

Question 28

Why does the national grid operate on a low current?

Answer 28

As electrons flow through a metal they collide with ions and transfer energy to them, increasing temperature and resistance which results in a loss of power to heating, operating on a low current means that less energy is lost

Question 29

What is the rule for current in a series circuit?

Answer 29

Current is the same everywhere in a series circuit due to the rule of conservation of current

Question 30

What is the rule for current at a junction?

Answer 30

Current entering the junction must equal the current leaving the junction due to the rule of conservation of charge and current

Question 31

The sum of emfs in a circuit loop = ?

Answer 31

The sum of voltages dropped across components in the circuit loop

Due to the law of conservation of charge

Question 32

What is a circuit loop?

Answer 32

Any path that can be taken by charges through a circuit

Question 33

What is a potential divider?

Answer 33

A series of resistors or components with resistance that split the way the potential difference is distributed around the circuit

Question 34

In a system with two resistors what is the potential difference over R1?

Answer 34

(Vs x R1) / (R1 + R2)

Question 35

Give an example of a potential divider

Answer 35

Rheostat

Question 36

Why are rheostats inefficient?

Answer 36

They result in a lot of power loss as they heat up quickly

Question 37

When might potential dividers be used?

Answer 37

In sensing circuits