Transcript How can you work out resistance in a circuit?

Additional Physics – Forces
Exam Date -
Potential
difference –
current graph
L/O :- To be able to recognise potential
difference – current graphs
Potential difference
– current graph
L/O :- To be able to recognise potential
difference – current graphs
Answers in the back of your books
1.How can you work out resistance in a circuit?
2.What affects the resistance in a wire?
3.What is the equation for working out current?
4.Does current split down branches of a parallel circuit?
5.Does voltage split down branches of a parallel circuit?
Potential difference
– current graph
L/O :- To be able to recognise potential
difference – current graphs
True or false:
1. The shorter the wire the lower the resistance.
2. The thicker the wire the lower the resistance.
3. The material of the wire can affect the resistance in
the wire.
4. The hotter the wire the higher the resistance.
5. The straighter the wire the lower the resistance.
Quick quiz
1.
2.
3.
4.
5.
What 2 factors affects your momentum?
How can you work out resistance in a circuit?
What affects the resistance in a circuit?
What is acceleration measured in?
What is the equation for work done and what is it
measured in?
6. What is the equation for working out current?
7. Name 3 things which can affect stopping distance
Time limit 5 minutes
Graph paper
• Plot the
results of
your
resistance
experiment.
Resistance in different materials
Vid clip
Ohm’s law
Ohm’s Law
The current through a resistor at constant
temperature is directly proportional to the potential
difference across the resistor
In other words; The current goes up at a constant rate with
the voltage {only under same temperature}
Resistance and Ohms Law
Video clip
Current (A)
0
Current (A)
Potential Difference (V) 0
You will need to be
able to recognise
this graph!
0.25
0.05
0.1
0.15
0.2
0.25
0.5
1
1.5
2
2.5
This resistor
supports Ohm’s
Law.
What does this graph tell you
about the relationship
between potential difference
and voltage in a resistor at a
constant temperature?
0.2
0.15
0.05
0
0.5
1
1.5
2
2.5
Potential Difference (V)
REMEMBER - Ohm’s Law
The current through a resistor at
constant temperature is directly
proportional to the potential
difference across the resistor
What do these graphs tell you about each component?
Filament Bulb
Diode
Get in pairs and write down what you can tell
from each graph?
What do these graphs tell you about each component?
Filament Bulb
Diode
REMEMBER – The flatter the graph the higher
the resistance
What do these graphs tell you about each component?
Filament Bulb
The filament bulb
follows ohms law at
low temperatures. At
higher currents the
temperature
increases, so it
doesn’t follow Ohms
law.
Diode
The diode has a
high resistance in
one direction. So it
resists the flow of
electrons in that
direction.
REMEMBER – you must be able to recognise
these graphs
• Diodes are electronic components that can be
used to regulate the potential difference in
circuits
• Light-emitting diodes (LEDs) give off light and
are often used for indicator lights in electrical
equipment
The diode has a very high resistance in one
direction – this means that current can only flow in
one direction
• The filament lamp is a common type of light bulb (it
contains a thin coil of wire called the filament)
• The filament heats up when an electric current passes
through it, and produces light as a result
The filament lamp does not follow Ohm’s Law – its
resistance increases as the temperature of its filament
increases. As voltage increases the bulb gets hotter, and
its resistance increases
What have you learnt?
• What do these graphs represent?