The document explains the concept of electrical resistance, including its dependence on factors like wire length, thickness, and material. It introduces Ohm’s Law, which describes the relationship between voltage, current, and resistance, providing practice problems for calculating current and voltage in circuits. Key terms and formulas are emphasized to help understand and calculate resistance in electrical components.

1. 9Jd-
Resistance
How can we calculate a
resistance of a
component?

2. Objectives
• Describe some factors that affect
resistance
• Use the formula relating voltage,
current and resistance.

3. Resistance
Today you will learn
what resistance is, and
how it can be useful in
electrical appliances,
some factors affecting
resistance and how to
work out the resistance
of a component by
measuring the current
and voltage across it.

4. Resistance is the opposition that an
electrical device has to the flow of
electrical current.
All devices have some resistance
Resistance

5. All devices
have some
resistance.
A resistor is a
device that has
a particular
resistance.
Resistors
Symbol for R
Resistance is measured in ohms

6. Georg Ohm

7. The resistance in a wire
depends on:
 Length of the wire
The shorter the length of the
wire, the less the resistance.

8. The resistance in a wire
depends on:
 Thickness (Cross Sectional Area) of the wire
A thicker wire offers less resistance
compared to a thinner wire.

9. The resistance in a wire
depends on:
 Type of material of the wire
Iron has more electrical resistance than
copper wire.

10. Ohm’s Law
V= I x R
Voltage (Volts)=
Current (Amps) times Resistance (ohms)
electric current is directly proportional
to voltage and inversely proportional to
resistance

11. Calculating resistance

12. Calculating resistance

13. Ohm’s Law Practice Problem
How much current is in a circuit with a 9
V battery and a light bulb with a
resistance of 3 ohms?
Current (A) Voltage (V) Resistance (Ω ) Formula Answer with
Unit
Looking for this
I= ?
9V 3Ω I = (V/R)
V divided by R

14. Ohm’s Law Practice Problem
How much current is in a circuit
with a 9 V battery and a light bulb
with a resistance of 3 ohms?
Truemper
10/24/20
11
Current (A) Voltage (V) Resistance (Ω ) Formula Answer with
Unit
Looking for this
I= ?
9V 3Ω I = (V/R)
V divided by R
3A

15. Ohm’s Law Practice Problem
What is the voltage of a circuit
with 15 A of current and a
toaster with 8 ohms of
resistance?
Truemper
10/24/20
11
Current (A) Voltage (V) Resistance (Ω ) Formula Answer with
Unit
15 A V= ? 8 V= I R

16. Ohm’s Law Practice Problem
What is the voltage of a circuit
with 15 A of current and a
toaster with 8 ohms of
resistance?
Current (A) Voltage (V) Resistance (Ω ) Formula Answer with
Unit
15 A V= ? 3 V= I R 45 V