Electric fields - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Electric fields

Electricity

Lesson 10 of 10

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up

Electricity

Lesson 10 of 10

Answer each one, then check.

1

What is a field?

2

Which charges attract?

3

What is a non-contact force?

4

What charge does an electron have?

5

What is a spark?

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up - Answers

Electricity

Lesson 10 of 10

1

What is a field?

A region where a force acts on certain objects

2

Which charges attract?

Unlike charges

3

What is a non-contact force?

A force between objects that are not touching

4

What charge does an electron have?

Negative

5

What is a spark?

A sudden flow of charge through air

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Learning Objectives

Electricity

Lesson 10 of 10

1

Explain the concept of an electric field.

2

Draw the electric field pattern for an isolated charged sphere.

3

Describe how the strength of the field changes with distance.

4

Explain non-contact forces and sparking using the idea of a field.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Electricity

Lesson 10 of 10

ELECTRIC FIELDS

A charged object creates an electric field around itself. A second charged object placed in the field experiences a force.

The field is strongest close to the charged object and gets weaker with distance. The force gets stronger as the distance between the objects decreases.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Field Around a Charged Sphere

Electricity

Lesson 10 of 10

Arrows show the direction of the force on a positive charge.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Drawing the Field of an Isolated Sphere

Electricity

Lesson 10 of 10

Follow the rules.

1

Draw the sphere

A circle with plus or minus signs.

2

Draw straight lines

At least 8 lines, evenly spaced, starting at the surface and going radially.

3

Add arrows

Away from a positive sphere; towards a negative sphere.

4

Show the strength

Lines are closer together near the sphere, where the field is stronger.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Force in a Field

Electricity

Lesson 10 of 10

A small positive charge is placed near a positively charged sphere. Describe the force on it and how it changes as the charge is moved closer.

1

Direction

The charge is repelled: the force is away from the sphere

2

As it moves closer

The field is stronger, so the force gets stronger

ANSWER

The force is repulsive and increases as the distance decreases.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Explaining a Spark

Electricity

Lesson 10 of 10

Explain how the idea of an electric field helps to explain sparking.

1

Charged object

Creates a strong electric field around itself

2

Air

The strong field can make air molecules lose electrons (ionise)

3

Charge flows

The ionised air conducts, so charge flows as a spark

ANSWER

A strong electric field ionises the air so charge can flow: a spark.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Non-Contact Forces

Electricity

Lesson 10 of 10

Fields explain forces at a distance.

Field

A charged object does not touch the other object, but its field acts on it.

Distance

The further away, the weaker the field and the force.

Direction

Field lines show the direction of the force on a positive charge.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Key Terms

Electricity

Lesson 10 of 10

Electric field

The region around a charged object where another charge feels a force.

Field lines

Lines showing the direction of the force on a positive charge.

Isolated sphere

A charged sphere far from any other charges.

Ionise

Remove or add electrons to make ions.

Non-contact force

A force between objects that are not touching.

Field strength

How large the force on a charge is at a point.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Electricity

Lesson 10 of 10

YOUR TASK

Draw the Field

12 minutes

Draw the electric field around (a) a positively charged sphere and (b) a negatively charged sphere. Show the arrows and how the strength varies.

1

Draw at least eight lines.

2

Add arrows in the right direction.

WHAT A GOOD ANSWER SHOWS

(a) Radial lines with arrows pointing away, closer together at the sphere. (b) Radial lines with arrows pointing towards the sphere.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Can I...?

Electricity

Lesson 10 of 10

Define an electric field.

Draw the field around a positive sphere.

Draw the field around a negative sphere.

Say how strength changes with distance.

Explain non-contact force with fields.

Explain sparking with fields.

Use arrows correctly.

Draw evenly spaced lines.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Summary & Exam Focus

An electric field surrounds a charged object.

Field lines point away from positive and towards negative.

The field is strongest close to the object.

A strong field can ionise air and cause a spark.

EXAM FOCUS

Draw the electric field pattern around an isolated negatively charged sphere. (2 marks)

Straight lines, arrows pointing towards the sphere.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Exam Practice: Electric fields

Electricity

Lesson 10 of 10

Answer all questions. Use the mark allocation as a guide to how much to write. · 14 minutes

Question 1 · 2 marks · Draw

Draw the electric field pattern of an isolated negatively charged sphere.

Question 2 · 3 marks · Complete the diagram

The diagram shows a positively charged sphere with two field lines drawn. Complete the diagram to show the electric field. Explain what the…

Question 3 · 2 marks · Explain

A small positive charge is moved towards a positively charged sphere. Explain how the force on the small charge changes.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Exam Practice: Electric fields (cont.)

Electricity

Lesson 10 of 10

Question 4 · 3 marks · Explain

Explain how the idea of an electric field helps to explain how a charged comb can pick up small pieces of paper without touching them.

Question 5 · 3 marks · Explain

Explain, using the idea of an electric field, how a spark can jump between a charged sphere and a metal rod.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 1 · 2 marks · Draw

Electricity

Lesson 10 of 10

“

Draw the electric field pattern of an isolated negatively charged sphere.

HOW TO ANSWER IT

Command word: Draw. Worth 2 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 1 · mark scheme

Electricity

Lesson 10 of 10

2 marks available. Award a mark for each point made.

Straight radial lines

1 mark

Arrows pointing towards the sphere

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 2 · 3 marks · Complete the diagram

Electricity

Lesson 10 of 10

The diagram shows a positively charged sphere with two field lines drawn. Complete the diagram to show the electric field. Explain what the diagram shows about the field strength. (3 marks)

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 2 · mark scheme

Electricity

Lesson 10 of 10

3 marks available. Award a mark for each point made.

Additional radial straight lines evenly spaced

1 mark

Arrows pointing away

1 mark

Field strongest close to the sphere

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 3 · 2 marks · Explain

Electricity

Lesson 10 of 10

“

A small positive charge is moved towards a positively charged sphere. Explain how the force on the small charge changes.

HOW TO ANSWER IT

Command word: Explain. Worth 2 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 3 · mark scheme

Electricity

Lesson 10 of 10

2 marks available. Award a mark for each point made.

Force increases as the distance decreases

1 mark

The field is stronger closer to the sphere

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 4 · 3 marks · Explain

Electricity

Lesson 10 of 10

“

Explain how the idea of an electric field helps to explain how a charged comb can pick up small pieces of paper without touching them.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 4 · mark scheme

Electricity

Lesson 10 of 10

3 marks available. Award a mark for each point made.

Charged object has an electric field

1 mark

The field exerts a force on other objects

1 mark

Non-contact force of attraction

1 mark

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 5 · 3 marks · Explain

Electricity

Lesson 10 of 10

“

Explain, using the idea of an electric field, how a spark can jump between a charged sphere and a metal rod.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

openrevise.com

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Question 5 · mark scheme

Electricity

Lesson 10 of 10

3 marks available. Award a mark for each point made.

Strong field near the sphere

1 mark

Ionises the air

1 mark

Charge flows through the air as a spark

1 mark

openrevise.com