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Electricity – interpreting graphs
Answers
1.
As potential difference increases, the current increases.
Which law is this graph illustrating? Ohm’s law.
The current through a metallic conductor at a constant temperature is
proportional to the potential difference.
2.
The straight lines show that resistance is constant.
Resistance = voltage ÷ current
The steeper the graph, the lower the resistance.
Resistor x has the highest resistance.
3.
Increasing temperature causes resistance in the thermistor to drop.
As temperature increases (as caused by a fire), the resistance of the thermistor
falls, allowing a current to flow and causing the alarm to sound.
4.
Current starts to flows when a small voltage is present.
e.g. Diodes prevent damage to battery powered equipment if a battery is put in
the wrong way round. The diode stops the current flowing in the wrong direction.
5.
Resistance decreases as light intensity increases. This causes the current to flow.
LDRs can be used to detect light levels. In bright light resistance in the LDR is low
therefore allowing current to flow.
6.
Resistance in the filament lamp is not constant.
As the temperature of the filament increases, the resistance increases.
As the temperature of the filament increases, its resistance increases, so the
current flowing through the lamp is not directly proportional to the voltage across
it.
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Electricity – interpreting graphs
Task
Answer the questions and fill in the gaps in each section.
1. Potential difference plotted As potential difference increases the
against current
................................................................
................................................................
current
(amps)
There is a relationship between the potential
difference and the current. Which law is this graph
illustrating?
................................................................
potential difference
(volts)
State the law
................................................................
................................................................
................................................................
2. Resistors
The graph shows two resistors.
The straight lines show that resistance is
constant/not constant.
Resistance= ....................... ÷ ......................
The steeper the graph the lower/higher the
resistance.
p.d.
(volts)
Resistor ................. has the highest resistance.
X
y
Current (amps)
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Electricity – interpreting graphs
3. Thermistor
What effect does an increase in temperature have on
the resistance of a thermistor?
..............................................................
resistance (ohms)
Explain how this can be used to make a fire alarm
work.
..............................................................
..............................................................
temperature
..............................................................
..............................................................
4. Diode
Current starts to flows when ..........................
current
..............................................................
current
flowing
in the
reverse
direction
Current flows in one direction only. Why is the
property useful and where are diodes used?
..............................................................
voltage
..............................................................
..............................................................
..............................................................
© www.teachitscience.co.uk 2012
19977
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Electricity – interpreting graphs
5. Light dependent resistor
(LDR)
Resistance increases/decreases as light intensity
increases. This causes the current to
..............................................................
resistance
Describe a use for a LDR and explain how it works.
..............................................................
..............................................................
..............................................................
Light intensity
..............................................................
6. Filament lamp
Resistance in the filament lamp is constant/not
constant.
current
As the temperature of the filament increases the
resistance increases/decreases.
Current flowing i
n the reverse
direction
Explain why a filament lamp does not follow Ohm’s
law.
..............................................................
..............................................................
voltage
..............................................................
..............................................................
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