Download 16.3 Resistance and Ohm`s Law

16.3 Resistance and Ohm’s
Law
Ohm’s Law Entrance Slip
A toaster has a resistance of
12 ohms and is plugged into a
120-volt outlet. How much
current does it draw?
Electrical Resistance
Resistance: how strongly a wire or other object resists
current flowing through it
low resistance = large current
high resistance = little current
Electrical Resistance
Every electrical device is
designed with a resistor that
causes the right amount of
current to flow when the
device is connected to
voltage.
A light bulb’s resistance
increases when there is more
current because the bulb gets
hotter when more current
passes through it.
Measuring Resistance
Resistors are used to control the current in circuits.
Resistance is measured
in ohms (Ω)
Measuring Resistance
Two types of resistors:
1. Fixed resistor: resistance cannot
be changed
2. Variable resistor (potentiometer):
resistance can be adjusted
Conductors and Insulators
Conductor: a material with
low electrical resistance
- examples: metals
Insulator: a material with
high electrical resistance
- examples: rubber, plastic
Ohm’s Law
The total amount of resistance in a circuit
determines the amount of current in the circuit for
a given voltage.
Ohm’s Law
Ohm’s Law Example

A battery supplies 3 V to a circuit and
a light bulb has a resistance of 2
ohms. What is the current in amperes?
Ohm’s Law Example

A current has two 9-V batteries that
supply energy to a light bulb with a
resistance of 6 ohms. How much
current runs through the circuit?
Ohm’s Law Example

A 1.5-V battery is used in a circuit with
a light bulb. If 6 amperes of current
runs through the circuit, what is the
resistance of the light bulb?
Ohm’s Law Example

Two 9-V batteries supply energy for
two light bulbs. If 3 amperes of
current runs through the system, how
much resistance does each light bulb
have?
Entrance Slip Revisited…
How’d you do? Look over your
entrance slip for today and see if
you change your answer. Take
two minutes…
A toaster has a resistance of
12 ohms and is plugged into a
120-volt outlet. How much
current does it draw?
Extra Example

A 3-V battery supplies energy to a
circuit with a light bulb that has 2
ohms of resistance. What is the
current?
Extra Example 2

You want a current of 10 amperes to
run through a circuit. The light bulb
has 6 ohms of resistance. How much
voltage must be supplied to the
circuit?