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Resistance

In this worksheet, students look at what resistance is, how it affects the electric current and how it is used.

Key stage:  KS 4

Curriculum topic:  Physics: Electricity

Curriculum subtopic:  Exploring Current, Resistance and Voltage Relationships

Difficulty level:  

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QUESTION 1 of 10

A resistor can be used to change the electric current (I) in a circuit. It can be a fixed resistor or a variable one (rheostat). The voltage (V) that a current produces depends on the resistance (R). The formula that connects current, voltage and resistance is:

 

The unit of resistance is ohm (Ω), current (ampere, A), voltage (volt, V)



Uses of resistance

A piece of wire has a resistance of 5 Ω and melts if the current through it exceeds 8 A. What is the maximum possible voltage that could cross the wire, without melting it?

To answer this, you need to rearrange the equation. For current, it would become: and for voltage it would be V = I x R. So, in our question V = 8 x 5 = 40 V

 

This is a picture of a resistor:

 

 

The current in a circuit must not be allowed to get too high. Electrons bump into the atoms of a resistor, which makes the atoms vibrate more and the resistor get hotter. This makes the flow of electrons difficult and resistance increases. Filaments (a tiny thin wire in a light bulb) becomes so hot that it emits light.

What can a resistor do?

it can change the electrical current in a circuit

it can split up current

it can create more current

Tick the two types of resistors.

fixed

split

variable

double

What do you divide voltage by to get resistance?

resistor

current

power

What do you need to divide the voltage by to get the current? Just write the word in the answer box below.

If the voltage is 6 V and the resistance 3 Ohm, how much is the current? 

2 A

2 V

2 Ohm

If the current is 6 A and the resistance is 5 Ohm, what is the voltage?

30 A

30 V

30 Ohm

If the current is 3 A and the voltage is 12 V, what is the resistance? 

4 Ohm

36 Ohm

0.25 Ohm

In the answer box below write the word which completes this sentence:

 

The current in a circuit must not be allowed to get too _______.

What happens to electrons when they meet atoms of a resistor?

they cool down

they slow down

they vibrate more

What happens to the resistor when its atoms vibrate more?

it splits up

it gets hotter

it gets colder

  • Question 1

What can a resistor do?

CORRECT ANSWER
it can change the electrical current in a circuit
EDDIE SAYS
Resistors can change the electrical current in a circuit.
  • Question 2

Tick the two types of resistors.

CORRECT ANSWER
fixed
variable
EDDIE SAYS
There are two types of resistors: fixed and variable. The variable resistor is known as a rheostat.
  • Question 3

What do you divide voltage by to get resistance?

CORRECT ANSWER
current
EDDIE SAYS
To work out the resistance, you need to divide voltage by current. Here is the formula again:
  • Question 4

What do you need to divide the voltage by to get the current? Just write the word in the answer box below.

CORRECT ANSWER
resistance
EDDIE SAYS
When you divide voltage by resistance you get the current:
  • Question 5

If the voltage is 6 V and the resistance 3 Ohm, how much is the current? 

CORRECT ANSWER
2 A
EDDIE SAYS
  • Question 6

If the current is 6 A and the resistance is 5 Ohm, what is the voltage?

CORRECT ANSWER
30 V
EDDIE SAYS
V = I x R = 6 x 5 = 30 V
  • Question 7

If the current is 3 A and the voltage is 12 V, what is the resistance? 

CORRECT ANSWER
4 Ohm
EDDIE SAYS
  • Question 8

In the answer box below write the word which completes this sentence:

 

The current in a circuit must not be allowed to get too _______.

CORRECT ANSWER
high
EDDIE SAYS
The current in a circuit must not be allowed to get too high, as the wire could melt.
  • Question 9

What happens to electrons when they meet atoms of a resistor?

CORRECT ANSWER
they vibrate more
EDDIE SAYS
Electrons bump into the atoms of a resistor, which makes the atoms vibrate more and the resistor get hotter. This makes the flow of electrons difficult and resistance increases.
  • Question 10

What happens to the resistor when its atoms vibrate more?

CORRECT ANSWER
it gets hotter
EDDIE SAYS
Electrons bump into the atoms of a resistor, which makes the atoms vibrate more and the resistor gets hotter.
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