Download Slide 1 - MrSimonPorter

Do now!
Can you
continue the
questions from
last lesson?
Last lesson
• Understand the term resistance
• Recall and use: V =IR
Resistance
Measures how difficult it is for current to
flow. Measured in Ohms (Ω)
V
Resistance = voltage/current
A
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 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.
Today’s lesson
• Understand the term power
• Recall and use: P =VI
Power
The amount of energy used by a device
per second, measured in Watts (Joules
per second)
A
V
Power = voltage x current
P = VI
Power
The amount of energy used by a device
per second, measured in Watts (Joules
per second)
A
V
☺
Can you copy
this please?
Power = voltage x current
P = VI
Power of a lamp
Measure the power of the lamp at it’s operating voltage.
What is the electrical energy being turned into?
A
V
Power = voltage x current
P = VI
Power of a lamp
Since P = VI, and V = IR, P = I2R = V2/R
V
A
Simple!
Let’s try some questions!
Homework
• Due 18th November (Wednesday)
• “Power” sheet
• Finish “Resistance” questions