Transcript (A) Resistance - Noadswood Science

Additional Physics – Forces
Exam Date -
LDR’s
L/O :- To know how LDR’s are affected by
light intensity
LDR’s
L/O :- To know how LDR’s are
affected by light intensity
Quick quiz:
1. What is the equation that relates current, charge and time.
2. What is the equation that relates Current, voltage and
resistance?
3. Why doesn’t a filament bulb obey Ohms Law?
4. What is the job of a diode?
5. Sketch a current voltage graph for a diode.
In Groups
• An LDR is a light dependant resistor.
• You shine a light at it and it either increases or decreases
in resistance.
• This is a good way of making electricity in a circuit
flow depending on light levels.
• Write down as many uses of a light dependant electronic
device as you can think of.
• The group with the most answers becomes Top Of The
Class
Quick experiment.
• You need to set up the circuit with an LDR and
shine the lamp at it at different distances.
• Draw a ‘SKETCH GRAPH’ of your results.
• Write out neatly in your books whether
resistance INCREASES or DECREASES with
more light.
TASK
1. Set up a circuit with a battery, ammeter, LDR and a
voltmeter across the LDR
2. Shine the lamp over the LDR and record the current
and voltage
3. Work out the resistance
4. Move the light 10cm away from the LDR and repeat
Distance of lamp
from LDR (m)
Light intensity
1/D2
0.1
100
0.2
25
0.3
11.1
0.4
6.25
0.5
4
Voltage (V)
Current (A)
Resistance (Ω)
http://www.youtube.com/watch?feature=endscr
een&NR=1&v=2n_vzqQXkkk
Graph your results, what do they tell you about
light intensity and the resistance of an LDR
How could you check the reproducibility of
your results
Light intensity vs resistance
• LDR
As the light level
increases
The resistance
decreases
THERMISTORS
A thermistor is a temperature dependent resistor.
How do you think
thermistors are
used in ovens and
fridges?
Next lesson:
Mid topic assessment:
It is a ‘how science works’ test. It doesn’t have very
many ‘recall’ questions; except;
The effects of adding LDRs and thermistors to a circuit.
(when is the resistance high and when is it low?)
The uses of LDR’s and thermistors.
Things that always seem to come up:
Types of error
How to describe a graph for 3 marks
The ‘how science works words’ on the yellow sheet at the
back of your books.