Ohm’s
Law
Ohm’s Law
Measuring Current
• Current is measured in unit amps (A)
2A
2A
2A
2A
1A
2A
1A
In a series circuit,
current is the same
at all the points
In a parallel circuit,
current is shared
between all the points
What is the current?
3A
3A
4A
1A
4A
1A
4A
1A
SERIES CIRCUIT
PARALLEL CIRCUIT
Measuring Voltage
• Voltage – the electrical push that a
cell/battery gives to the current
• Voltage is also known as Potential
Difference
• Voltage is measured in unit volts (V)
Measuring Voltage
3V
3V
3V
1.5V
1.5V
In a series circuit,
voltage is shared
between all the points
3V
In a parallel circuit,
voltage is the same at
all the points
What is the current and voltage?
6V
4A
A
4A
V
3V
V
3V
A
4A
Current Voltage
Series Same
Shared
Parallel Shared Same
What is the current and voltage?
4A
6V
A
4A
V
6V
A
2A
V
6V
A
2A
Measuring Resistance
•
Resistance – slows down current, adding
components to a circuit increases resistance
•
Resistance is measured in unit ohms (Ω)
•
More resistance = Less current = Less light
In a series circuit, add all resistors to get total
Electrical Power
What is the current?
What is the current?
What is the current?
How much voltage gives 5
amps of current through
a 3 Ω light bulb?
I = V/R
V = (5A)  (3Ω)
V = 15V
How much current flows in a
circuit with a 1.5 volt battery
and three 1 ohm resistances
(bulbs) in series?
I = V/R
I = (1.5V) / (3Ω)
I = .5A
What is the voltage drop
across each resistor in the
circuit?
In a series
circuit,
voltage is
shared
between all
the points
9V/3 = 3V
A light bulb with a resistance of
1.5Ω is connected to a 1.5V
battery in the circuit. Calculate
the power used by the light bulb?
P = IV
I = V/R
I = (1.5V) ÷ (1.5Ω)
I = 1A
P = (1A)  (1.5V)
P = 1.5 W