9.3 Resistance

• Physics
• Secondary Education
• Age 12,13

27 April 2023

Unit 9.3 Resistance

Content objectives

• I can explain the effect of resistance to current in a circuit.
• I can state the equation that links voltage, current, and resistance (Ohm's Law).
• I can use Ohm's law to calculate resistance from voltage and current.

What have I learned?

• Describe how current flows in a conductor.
• Describe the difference between a conductor and an insulator regarding current flow.
• What does the word resistance mean in everyday language?

Resistance

• a measure of how easy or difficult it is for electrons to move through a material
• Symbol: R
• measured in units called "ohms" or Ω 

Which of the following is a conductor?

plastic

wood

Which of the following has the lowest resistance?

copper

plastic

wood

Example

• A 100 m length of copper can have a resistance of 0.5-1.0 Ω.
• A 1-cm length of plastic can have a resistance of 1000000000000 Ω.

What does resistance do?

1. slows down the flow of electrons
2. makes current higher

Why is the wire covered with plastic?

Conductors in light bulbs

• Some conductors are designed to have high resistance. WHY?

Conductors in light bulbs

• Some conductors are designed to have high resistance. WHY?

filament

As resistance makes it difficult for current to flow ____________.

the greater the resistance in a circuit

the lesser the resistance in a circuit

The greater the resistance in a circuit, the __________ the current flow

smaller

bigger

low

high

easy

Do this in your notebook.

Ohm's Law

• Georg Simon Ohm
• link between voltage, current, and resistance
• resistance applies to many electrical components not only wires

Using an equation, what does Ohm's Law say?

Using an equation, what does Ohm's Law say?

Resistors

• a type of electrical component designed to have a known resistance
• colours in these resistors for a code to show the resistance value in ohms.

Do this in your notebook.

26 April 2023

Unit 9.2 Current and Voltage in parallel circuits

What do I call these devices?

What do I call the devices shown?

How are these devices connected in a circuit?

Ammeter -

Voltmeter -

Voltage in a SERIES circuit

Voltage in a SERIES circuit

Adding more components in a Series circuit

Adding more components in a Series circuit

Adding more components in a Series circuit

What happens to the current in a series circuit if you increase the number of cells?

1. current increases
2. current decreases

What happens to the voltage in a series circuit if you increase the number of cells?

1. Voltage increases across each component.
2. Voltage decreases in the battery.

Voltage in a PARALLEL circuit

What do you notice in these diagrams?

Adding more components in a Parallel circuit

Adding more components in a Parallel circuit

What happens to the supply voltage in a parallel circuit if you increase the number of cells?

1. supply voltage increases
2. supply voltage decreases

What happens to the voltage across each branch in a parallel circuit if you increase the number of cells?

1. voltage increases
2. voltage decreases

What happens to the current through the cell in a parallel circuit if you increase the number of cells?

1. current through the cell increases
2. current through the cell decreases

What happens to the current through each branch in a parallel circuit if you increase the number of cells?

1. current through each branch increases
2. current through each branch decreases

Practice Activity

voltage

parallel

series

current

Classwork Activity

What's next?