What affects the current in a wire

1
What affects the current in a wire?

• The information here may help you in your GCSE
  coursework
• It may also help you understand some important
  ideas about electricity for your GCSE exams

2
What model can we use for electrical current?

• We can imagine a current being like water flowing
  in a pipe.
• A pump pushes the water around the pipe
• The pump does not make water it simply moves it
  around the circuit.
• The pump acts in the same way as a battery acts
  in a circuit.

3
Are there any problems with this model?

• If a water pipe is broken then water escapes.
• If an electrical circuit is broken electrical
  charge does not escape, the current simply stops.

4
Can we improve our model of current?

• Any model of current must include a physical
  substance that flows in a circuit.
• We now need to look more closely at the structure
  of metal conductors to understand what is moving
  in a real circuit.

5
What is inside a metal?

• You should know that metals contain a regular
  arrangement of particles.

• To understand why metal conducts we must know
  about two types of particles in a wire

6
What is inside a wire?

• There is a fixed arrangement of positive ions.

And a "sea" of free electrons, which carry
negative charge.
7
What is inside a wire?

• Normally the electrons in a metal have random
  motion.

• There is no net movement of charge from one place
  to another.

8
What happens when a current flows?

• A battery or other voltage source causes the
  electrons to drift in one direction.

• The electrons are attracted to the positive side
  of the battery.

9
How Can We Measure The Current In A wire?

• As a starting point we must have a wire and power
  supply
• But without an ammeter we cant measure the
  current

• A voltmeter will allow us to measure the voltage
  more accurately

10
What problems may occur while measuring the
current ?
V
A
11
What problems may occur while measuring the
current ?

• The wire may overheat

V
2V DC
A
12
What problems may occur while measuring the
current ?

• The wire may overheat
• The current may be too small to measure
  accurately

V
0.02 A