Download Lesson 6 Resistance

Do now!
Can you
continue the
graphs from
yesterday?
Last lesson
• Understand that voltage is the number of
joules per coulomb transferred
• Looking at voltage in different circuits
Voltage(emf)
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☺
☺
V
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☺
☺
I’m checking the
difference in
energy (per
coulomb) between
the 2 red arrows
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1 Volt = 1 Joule per coulomb
Voltage (p.d.)
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I’m checking the
difference in
energy (per
coulomb) before
and after the lamp
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V
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1 Volt = 1 Joule per coulomb
Stand
up!
In a series circuit
The sum of the voltages across the lamps
equals the voltage across the cells
9V
3V
3V
3V
In a series circuit
The sum of the voltages across the lamps
equals the voltage across the cells
9V
☺
3V
3V
3V
Can you copy
this please?
Stand
up!
In a parallel circuit
In a simple parallel circuit, voltage across
each lamp equals the voltage across the
cells
5V
5V
5V
In a parallel circuit
In a simple parallel circuit, voltage across
each lamp equals the voltage across the
cells
5V
5V
☺
5V
Can you copy
this please?
Today’s lesson
• Understand the term resistance
• Recall and use: V =IR
Stand
up!
Resistance
Measures how difficult it is for current to
flow. Measured in Ohms (Ω)
V
Resistance = voltage/current
A
R = V/I
Resistance
Measures how difficult it is for current to
flow. Measured in Ohms (Ω)
V
☺
A
Can you copy
this please?
Resistance = voltage/current
R = V/I
Ohm’s Law
• V = IR
V
I
X
☺
R
Can you copy
this please?
Let’s
measure a
resistance!
Resistance of a lamp
Vary the voltage and current using a variable resistor
(rheostat). Plot a graph of resistance against current
V
Resistance = voltage/current
A
R = V/I
Resistance of a lamp
V(V) I(A)
R(Ω)
R(Ω)
I(A)
Resistance of a lamp
• As the current in a lamp increases, it gets
hotter, and its resistance increases. Why?
Resistance of a lamp
• As the current in a lamp increases the
electrons collide with the atoms in the wire
making them vibrate (get hot). This
vibration makes it harder for the electrons
to travel in the wire and so the resistance
increases.
• YouTube - Electricity 4 ResistanceRelated
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Gather around
Mr Porter
Let’s try some questions