Resistance ISA
Here’s the plan:
• Thurs 20th – Graph of current against resistance.
Theory of heat/resistance.
• Friday 21st – Background, context, research, CRN.
• Mon 24th – CRN (continued) Table and Paper 1 Prep
• Tues 25th – Paper 1
• Wed 26th – Practical (am), Graph (pm)
• Fri 28th – Paper 2 Prep
• Mon 1st – Paper 2 Prep (again!)
• Tues 2nd – Paper 2? (it’s a pm lesson)
• Wed 3rd – Paper 2?
The Background
Filament lamp symbol
The filament lamp is a common type
of light bulb. It contains a thin coil of
wire called the filament.
This heats up when an electric
current passes through it and
produces light as a result.
Higher tier only
An electric current flows when electrons
move through a conductor, such as a metal
wire.
The moving electrons can collide with the
ions in the metal. This makes it more difficult
for the current to flow, and causes
resistance.
As the temperature increases, the metal ions
vibrate more. There are more collisions with
the electrons and so the resistance
increases.
Electricity in wires is a flow of electrons along the wire. As the electrons
move along the wire they collide with the copper atoms (ions). These
collision make the atoms vibrate more…which makes the metal hotter.
This in turn, leads to more collisions, and therefore more resistance.
Resistance is a measure of how much a material ‘tries’ to stop
electricity passing through it.
The Context Part 1: When you first
switch on a filament bulb:
1. The filament wire is cool.
2. The resistance is low, so this causes a high
current to flow.
3. The high current leads to a ‘surge’, which in turn
causes resistance to increase.
4. The surge only lasts 0.1 s, but causes the
filament wire to heat up suddenly, called
‘thermal shock’.
5. This may cause the wire to melt and break at a
weak point.
The Context Part 2
• Consumers (that means ordinary people) want
light bulbs that can be switched on and off
thousands of times without the bulb blowing.
• Light bulb manufacturers need to know how the
resistance in a bulb changes as the current
changes.
• HT: This will help them design bulbs that can
withstand the high resistance that occurs when
bulbs suddenly heat up when first switched on, to
avoid them blowing.
Your hypothesis…
• You need to come up with this on your own.
• Basic format: ‘I think that if I change ‘x’ then
‘y’ will ………..’
• Hint: Mention current and resistance,
increase and/or decrease.
Research
• Use the 4 resources provided to get further
information and give you ideas on how to test
your hypothesis.
• You may also want to look back at the
practical we did last week.
Candidate Research Notes
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•
•
•
•
• Hypothesis: ‘I think that if I change ‘x’ then ‘y’ will ………..’
• Sources: Where did you find your information. You must be
specific – the full website address / title and author of the
textbook to get 3 marks you need to be able to explain why
you chose one source, what was better about it, why you
rejected the other one and what was less good about it.
Method: Write up neatly as a list of notes to remind you in the
exam
Equipment: A list of what you’ll need
Risk Assessment: any possible hazards / risks /controls - table
Context: Light Bulb Manufacturers.
Light bulbs need to able to withstand being switched on and off
hundreds of times without the bulb blowing.
Planning your method….
 Method
A short list of instructions in note form in order, not
written in sentences- spellings must be perfectly
correct!!!
The equipment that is needed for the experiment - a list - spellings again!
What are your independent, dependent and control
variables?
Risk Assessment What are the potential Hazards,
Risks and Control Measures involved in the
experiment – put it in a table!