Current Electricity

Question 1

What happens when insulating materials are rubbed together?

Answer 1

Certain insulating materials become charged when rubbed together.

Question 2

What is transferred when objects become charged?

Answer 2

Electrons are transferred:

• insulating materials that become positively charged when rubbed lose electrons
• insulating materials that become negatively charged when rubbed gain electrons

Question 3

What happens when charges are brought together?

Answer 3

Like charges repel.

Unlike charges attract.

Question 4

What is a cell?

Answer 4

It is necessary to push electrons around a complete circuit.

Question 5

What is a battery?

Answer 5

It consists of two or more cells.

Question 6

What is a switch?

Answer 6

It enables the current in a circuit to be be switched on/off.

Question 7

What is an indicator?

Answer 7

• emits light as a signal when a current passes through it

* light source

Question 8

What is a diode?

Answer 8

It allows current through one directions only.

Question 9

What is a light-emitting diode (LED)?

Answer 9

It emits light when a current passes through it.

Question 10

What is an ammeter?

Answer 10

It is used to measure electric current.

Question 11

What is a fixed resistor?

Answer 11

It limits the current in a circuit.

Question 12

What is a variable resistor?

Answer 12

It allows the current to be varied.

Question 13

What is a fuse?

Answer 13

It melts and therefore breaks the circuit if the current through it it greater than a certain amount.

Question 14

What is a heater?

Answer 14

It transfers electrical energy to heat the surroundings.

Question 15

What is a voltmeter?

Answer 15

It is used to measure potential difference.

Question 16

What is the size of an electric current?

Answer 16

The rate of flow of electric charge.

Question 17

What is electric current?

Answer 17

The flow of charge.

Question 18

How can we calculate the size of an electric current?

Answer 18

Current (A) = charge flow (C) / time taken (s)

Question 19

What is potential difference?

Answer 19

A measure of the work done or energy transferred to the lamp that passes through it.

Question 20

How do we measure the potential difference?

Answer 20

Potential difference (V) = work done (J) / charge (C)

Question 21

What is resistance?

Answer 21

Resistance (ohms) =potential difference (V) / current (A)

Question 22

What is Ohm’s law?

Answer 22

The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor.

Question 23

What happens if you reverse the current in a resistor?

Answer 23

Reversing the current through a component reverses the potential difference across it.

Question 24

Why is a wire an panic conductor?

Answer 24

It’s resistance is constant.

Question 25

What happens to the resistance of a filament bulb as its temperature increases?

Answer 25

The resistance increases with increases of the filament temperature.

Question 26

How does the current through a diode depend on on the potential difference across it?

Answer 26

In the 'forward' direction, the resistance is low. | In the 'reverse' direction, the resistance is high.

Question 27

What happens to the resistance of a thermistor as its temperature increases?

Answer 27

The resistance decreases if its temperature increases.

Question 28

What happens to the resistance of a light-dependent resistor (LDR) as the light level increases?

Answer 28

The resistance decreases if the light intensity on it increases.

Question 29

Where are thermistors and LDRs used?

Answer 29

In sensor circuits.

Question 30

What happens to the current in series circuits?

Answer 30

The same current passes through components in series with each other.

Question 31

What happens to the potential difference of the voltage supply in series circuits?

Answer 31

The total potential difference of the voltage supply in a series circuit is shared between the components.

Question 32

What happens to the potential difference of cells in series circuits?

Answer 32

The total potential difference of cells in series is the sum of the potential difference of each cell.

Question 33

How can we find the total resistance of resistors in series?

Answer 33

The total resistance of components in series is equal to the sum of the resistance of each component.

Question 34

How can we calculate the current though a resistor in a parallel circuit?

Answer 34

Current (A) = potential difference (V) / resistance (ohms)

Question 35

What can we say about the currents in the components in a parallel circuit?

Answer 35

* the total current is the sum of the currents through the separate components * the bigger the resistance of a component, the smaller its current is.

Question 36

What can we say about the potential difference across the components in a parallel circuit?

Answer 36

The potential difference is the same across each component.