resistance ohm's law

1. 09/10/2016
PHYSICS
RESISTANCE
OHM’S LAW

2. V, I, R equations (OHM’S LAW)
Resistance( R ) = potential difference ( V )
current ( I )
Where:
Resistance R is measured in ohm
Potential difference (p.d) is measured in
volt (V)
Current( I ) is measured in ampere (A)
If R = V
I
Then:
V = IR and I = V
R

3. Resistivity of material
=
Comparing wires A and B made from the same material,
the resistivity (rho) is the same
For each wire at a particular temperature.
Resistance(A) X area(A) = resistance(B) X area(B)
length(A) length(B)

4. Series circuits
These lamps are connected in
series
• They share voltage from the
battery so each shines dimly
• If one lamp is removed, the
other goes out because the
circuit is broken.
When resistors are connected
in series:
• The current in each of the
components is the same
• The total p.d across all the
components is the sum of the
p.ds across each of them.
• R = R1 +R2 +R3

5. Parallel circuit
These lamps are connected in parallel:
• Each get full p.d from the battery
because it is connected directly
to it. So each sines brightly.
• If one lamp is removed, the other
keeps working, because it is still
part of an unbroken circuit.
When resistors are connected in
parallel:
• The p.d across each of the
component is the same
• The total current in the main circuit is
the sum of the current in the
branches

6. • 1 = 1 + 1 + 1
R R1 R2 R3
Used for more than two
resistors connected in parallel
Used for only two resistors
connected in parallel.