Transcript Static Charge to Electric Current - science

21 July 2015
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Sketch the graphs and describe whatI
they show.
Ohm’s Law
Objectives
Be able to describe what resistance is
and calculate it.
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HSW: AF4 – Using investigative approaches
Used before in: Energy,
Will use again in: lesson
Work and Momentum
6 – Non-Ohmic devices
PLTS: Team workers – Work collaboratively with
others.
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Used before in: lesson 4 Will use again in: lesson
– circuits
6 -Non-Ohmic devices
Keywords
Current (I), Amp, Voltage (V), Volts, ammeter, voltmeter,
resistor, variable resistor, resistance (R), Ohm, directly
proportional.
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OUTCOMES
• All students should be able to describe that
resistance restricts the flow of current and
understand that resistors add in series.
• Most students should be able to test circuits for
current and potential difference and describe
Ohm’s Law and use the definition of resistance
in calculations.
• Some students should be able to interpret
graphs that relate to current-potential difference
and describe resistance in terms of ions and
electrons.
Resistance Song
Resistance
Resistance is the opposition
that an electrical device has
to the flow of electrical
current.
All devices have some
resistance. A resistor is a
device that has a particular
resistance.
a resistor
circuit symbol for
a resistor
Resistance equation
resistance = potential difference
current
Where:
potential difference is in volts (V)
current is in amperes (A)
resistance is in ohms (Ω)
Also:
potential difference = current x resistance
and:
current = potential difference
resistance
potential
difference
current
resistance
Measuring Resistance
The resistance of a
component can be
found by measuring
the current through,
and potential
difference across,
the component.
Circuit used for measuring the
resistance of an indicator lamp
Example
Calculate the resistance of a lamp if a
potential difference of 12V causes a current
of 3A to flow through the lamp.
resistance = potential difference
current
= 12V / 3A
resistance = 4 ohms (4Ω)
Complete:
Answers
potential
difference
20 V
current
resistance
4A
5Ω
200 V
5A
40 Ω
300 V
8V
6A
500 mA
16 Ω
3 kV
20 A
150 Ω
120 V
4 mA
30 kΩ
50 Ω
Current-potential difference graphs
These are used to show
how the current through
a component varies with
the potential difference
across it.
The circuit opposite
could be used to obtain
a current-potential
difference graph of a
wire.
Current-Potential Graph of a
Wire/Resistor
• Set up the equipment as shown:
Results
Potential
Difference, V
(V)
• Vary the PD and take readings
of current.
• Analysis
• Once you have a set of results
draw a graph of Current on the
y-axis and PD on the x-axis and
write a conclusion.
Current, I (A)
The current-potential difference graph
of a resistor at a constant temperature
The graph is a straight line
through the origin.
The graph shows that the
current through a resistor is
directly proportional to the
potential difference across
the resistor.
Typical results:
Ohm’s Law
• Ohm’s Law says that current is directly
proportional to voltage when the
temperature of the conductor is constant.
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If the current is reversed then
the pattern stays the same:
Choose appropriate words to fill in the gaps below:
current
An electric ________
will only flow around a circuit if there
are no ______
gaps in the circuit.
resistance
All components have __________.
The greater the resistance
smaller is the current for the same applied potential
the ________
difference. Resistance is measured in ______.
ohms
A current – potential difference graph for a ________
resistor is a
origin
straight line through the _______.
This shows that the
proportional to the applied
current through the resistor is ___________
potential difference.
WORD SELECTION:
smaller resistor
proportional
gaps
origin resistance ohms current
Tell me two things...
(for each)
• that you have done well this session
• that you know now that you didn’t
know at the start
• that you could do better next time
• that you would like to know more
about