4.2.1 Current, potential difference and resistance

Question 1

Draw the circuit symbol for a cell.

Answer 1

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Question 2

Draw the circuit symbol for a battery.

Answer 2

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Question 3

Draw the circuit symbol for a lamp.

Answer 3

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Question 4

Draw the circuit symbol for a fuse.

Answer 4

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Question 5

Draw the circuit symbol for a voltmeter.

Answer 5

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Question 6

Draw the circuit symbol for an ammeter.

Answer 6

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Question 7

Draw the circuit symbol for a diode.

Answer 7

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Question 8

Draw the circuit symbol for a resistor.

Answer 8

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Question 9

Draw the circuit symbol for a thermistor.

Answer 9

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Question 10

Draw the circuit symbol for a variable resistor.

Answer 10

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Question 11

Draw the circuit symbol for an LDR.

Answer 11

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Question 12

Draw the circuit symbol for an LED.

Answer 12

[Image not displayed, but the instruction is to draw the circuit symbol.]

Question 13

What is electric current?

Answer 13

The flow of electrical charge.

Question 14

State the equation linking charge, current and time. Give the units for the quantities involved.

Answer 14

Q = I tCharge (Coulombs), Current (Amperes), Time (Seconds)

Question 15

What can be said about the value of current at any point in a single closed loop?

Answer 15

Current is the same at all points in a closed loop.

Question 16

What two factors does the current in a circuit depend on?

Answer 16

Potential Difference (V) Resistance (R)

Question 17

What equation should be used to calculate potential difference if current and resistance are known? State the units for all 3 quantities.

Answer 17

V = I RPotential Difference (V), Current (A), Resistance (Ω)

Question 18

What is an ‘Ohmic Conductor’? State the condition required.

Answer 18

● A conductor for which current and potential difference are directly proportional● Resistance remains constant as current changes● Temperature must be constant

Question 19

List four components for which resistance is not constant as current changes.

Answer 19

Lamps Diodes Thermistors Light Dependant Resistors (LDRs)

Question 20

What happens to the resistance of a filament lamp as the temperature increases? Why?

Answer 20

● Resistance increases● Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow

Question 21

What is different about current flow through a diode?

Answer 21

● The current only flows in one direction● Resistance is very high in the other direction, preventing current flow

Question 22

State what happens to the resistance of a thermistor as temperature increases.

Answer 22

The thermistor’s resistance decreases.

Question 23

Give two examples of when a thermistor may be used.

Answer 23

In a thermostat to turn a heater on below a certain temperature In a freezer to turn on a cooler when the temperature becomes too high

Question 24

State what happens to the resistance of a LDR as light intensity decreases.

Answer 24

The LDR’s resistance increases.

Question 25

Give an application for a LDR.

Answer 25

● Street lights often use LDRs● When light levels become too low, the light gains sufficient current to turn on

Question 26

What is the unit of **current**?

Answer 26

Amperes (Amps) ## Footnote Amperes measure the flow of electrical charge.

Question 27

What is the unit of **charge**?

Answer 27

Coulomb ## Footnote Coulomb is the standard unit for measuring electrical charge.

Question 28

Define **Electrical Current**.

Answer 28

The rate of flow of electrical charge ## Footnote Its value is the same at any position in a single closed loop.

Question 29

What is **Potential Difference**?

Answer 29

The product of a component’s resistance and the magnitude of current flow through it ## Footnote It is measured in volts.

Question 30

What does **Resistance** measure?

Answer 30

Opposition to current flow ## Footnote It is measured in ohms.

Question 31

What is the unit of **resistance**?

Answer 31

Ohms ## Footnote Ohms quantify how much a component resists the flow of current.

Question 32

What is an **Ohmic Conductor**?

Answer 32

A conductor whose current flow is directly proportional to the potential difference across it ## Footnote This relationship holds when the temperature is constant.

Question 33

What is **Electrical Work**?

Answer 33

When charge flows in a circuit, electrical work is said to be done ## Footnote It relates to the energy transferred by the flow of charge.

Question 34

What is a **Diode**?

Answer 34

A component that only allows current to flow through in the forward direction ## Footnote Diodes have very large resistances in the reverse direction.

Question 35

What is a **Filament Lamp**?

Answer 35

A light emitting component consisting of an enclosed metal filament ## Footnote Its resistance increases as the filament’s temperature increases.

Question 36

What does **Light Dependent Resistor (LDR)** do?

Answer 36

A light sensitive component whose resistance increases as its temperature decreases ## Footnote LDRs are used in various light-sensing applications.

Question 37

What is a **Thermistor**?

Answer 37

A temperature dependent component whose resistance increases as its temperature decreases ## Footnote Thermistors are commonly used in temperature detection.

Question 38

What is the **Live Wire** in a mains power supply?

Answer 38

The brown coloured wire that carries the alternating current from the supply ## Footnote It is responsible for delivering power to appliances.

Question 39

What is the **Neutral Wire**?

Answer 39

The blue coloured wire that completes the circuit in a mains power supply ## Footnote It carries current away from the appliance.

Question 40

What is the purpose of the **Earth Wire**?

Answer 40

Prevents an appliance from becoming live ## Footnote It is green and yellow striped for safety.

Question 41

In a **Series Circuit**, how is the current distributed?

Answer 41

The same current passes through each component ## Footnote Total potential difference is shared across components.

Question 42

In a **Parallel Circuit**, how is the potential difference distributed?

Answer 42

The same potential difference across each component ## Footnote Total current is equal to the sum of the currents through each branch.

Question 43

What is the formula for calculating **current**?

Answer 43

Q=It ## Footnote Q is charge in coulombs, I is current in amperes, and t is time in seconds.

Question 44

What is the relationship between **current**, **resistance**, and **potential difference**?

Answer 44

I = V/R ## Footnote Current through a component depends on both resistance and potential difference.

Question 45

True or false: **Ohmic conductors** have a constant resistance.

Answer 45

TRUE ## Footnote Their current is directly proportional to the potential difference, resulting in a linear graph.

Question 46

What happens to resistance with **increased current**?

Answer 46

Resistance increases, current decreases ## Footnote More current causes electrons to collide more with atoms.

Question 47

What is the effect of **temperature** on resistance in normal wires?

Answer 47

Resistance increases as temperature increases ## Footnote Atoms vibrate more, leading to higher resistance.

Question 48

How does **length** affect resistance?

Answer 48

Longer wire → resistance increases ## Footnote Electrons encounter more atoms, leading to higher resistance.

Question 49

What happens to the resistance of an **LDR** in light?

Answer 49

Resistance decreases ## Footnote In darkness, resistance is highest, making LDRs useful in automatic night lights.

Question 50

What is the **National Grid**?

Answer 50

Connects power stations to consumers ## Footnote It includes transformers to manage voltage levels for safety and efficiency.

Question 51

What is **static electricity**?

Answer 51

Charge that builds up on insulators due to electron transfer ## Footnote Rubbing insulators can create static charges.

Question 52

What is the behavior of **like charges**?

Answer 52

Repel each other ## Footnote Opposite charges attract each other.

Question 53

What do **electric fields** represent?

Answer 53

Regions around charged objects where electric forces are exerted ## Footnote They point away from positive charges and towards negative charges.