Current + Voltage In Circuits

Question 1

What is the flow of charge called

Answer 1

Electric current

Question 2

Insulators

Answer 2

All electrons are held tightly in position, unable to move from atom to atom

Charges unable to move through insulators

Question 3

What does an ammeter measure

Answer 3

Current

I in amps

Question 4

What is electric charge measured in

Answer 4

Coulombs

Question 5

Charge equation

Answer 5

Charge (Coulombs) = current x time

Question 6

What does a voltmeter measure

Answer 6

Voltage in volts

Question 7

Energy transferred equation

Answer 7

Energy transferred (joules) = charge x voltage

Question 8

‘Single loop’ circuit

Answer 8

Series circuit

Question 9

More than one path circuit

Answer 9

Parallel circuit

Question 10

In a series circuit…..

Answer 10

• current same

- voltage splits

Question 11

In a parallel circuit

Answer 11

• current splits

- voltage same

Question 12

What does Ohm’s law state ?

Answer 12

The resistance of a component is given by voltage/current and for a resistor is constant at a constant temp

Question 13

For a given resistor….

Answer 13

More voltage gives more current

Question 14

For a given voltage……

Answer 14

A larger resistance has a smaller current

Question 15

Resistance equation

Answer 15

Resistance = voltage/current

Resistance = in ohms

Question 16

For a fixed resistance…..

Answer 16

Current is proportional to voltage

Question 17

For a metal filament lamp…..

Answer 17

Resistance increases when current increases

Question 18

For a diode…..

Answer 18

In reverse direction (infinite resistance and no current)

In forward direction (small resistance)

Question 19

Resistance of a thermistor

Answer 19

The resistance of the thermistor decreases if the temp increases

Question 20

Experiment for thermistor:

Answer 20

1) measure initial temp of the water (thermometer), record one voltage a current
2) repeat this changing the temp of the water each time, record voltage and current each time
3) using the equation voltage/current, work out resistance
4) plot a graph of resistance against temp

Question 21

Experiment for light dependant resistor (LDR):

Answer 21

1) use a ‘light meter’ to measure light intensity

2) vary the distance the bulb is from the LDR, or vary the brightness of the bulb

Question 22

As light intensity increases…..

Answer 22

Resistance decreases (non linear)

Question 23

What do LDR and thermistor act as?

Answer 23

Sensors, they respond (automatically) to an external property

Question 24

How to answers question about LDR or thermistor?

Answer 24

1) pick a change
2) say how the resistance of the device changes
3) say how the current through the circuit changes
4) say what happens to the output device
5) give a practical use of the circuit

Question 25

Thermistor example answer

Answer 25

As temp rises, resistance of thermistor falls, Current in circuit rises, Bulb comes on

Use: alert to show when a temp of a soldering iron is too hot

Question 26

Use of an LDR

Answer 26

Alarm to show when a light in a photographic dark room gets too bright

Question 27

Current + charge equation

Answer 27

Current = charge flowing / time taken

Question 28

Energy + voltage equation

Answer 28

Energy transferred = charge x voltage

Question 29

Volts equation

Answer 29

Volts = joules / coulombs

Question 30

What is a volt

Answer 30

1 volt = 1 joule per coulomb

Question 31

What is DC

Answer 31

Direct current

Current that flows in one direction

Question 32

What is AC

Answer 32

Alternating current

Current constantly changing direction

Question 33

UK mains voltage and frequency?

Answer 33

Voltage = 230 V
Frequency = 50Hz

Question 34

What current does uk mains work on

Answer 34

AC

Question 35

What is a safe voltage for uk mains?

Answer 35

50V