Life cycle of a star - Teacher Slides.pptx

AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Life cycle of a star

Space physics

Lesson 2 of 4

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up

Space physics

Lesson 2 of 4

Answer each one, then check.

1

What does the Sun produce?

2

What force pulls matter together?

3

What is fusion?

4

What is the main element in stars?

5

What is a star?

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Warm-up - Answers

Space physics

Lesson 2 of 4

1

What does the Sun produce?

Light and heat

2

What force pulls matter together?

Gravity

3

What is fusion?

Nuclei joining together to form a larger nucleus

4

What is the main element in stars?

Hydrogen

5

What is a star?

A huge ball of hot gas

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Learning Objectives

Space physics

Lesson 2 of 4

1

Describe the life cycle of a star like the Sun and of a star much more massive than the Sun.

2

Explain how a stable main-sequence star is formed and how it stays stable.

3

Explain how fusion in stars forms the elements.

4

Explain how elements heavier than iron are formed.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Space physics

Lesson 2 of 4

STARS

A star forms from a nebula pulled together by gravity. In the main sequence, the inward force of gravity is balanced by the outward pressure from fusion energy, so the star is stable. When the hydrogen runs out, the star changes.

The mass of a star decides how it ends: a star like the Sun becomes a white dwarf; a much more massive star explodes as a supernova.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

The Life Cycle of Stars

Space physics

Lesson 2 of 4

Mass decides the path after the main sequence.

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Sun-sized or Massive?

Space physics

Lesson 2 of 4

A STAR LIKE THE SUN

• Nebula, protostar, main sequence.

• Expands to a red giant.

• Outer layers drift away; the core shrinks to a white dwarf.

• Cools to a black dwarf.

A MUCH MORE MASSIVE STAR

• Nebula, protostar, main sequence.

• Expands to a red supergiant.

• Explodes as a supernova.

• Leaves a neutron star or a black hole.

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Why a Main Sequence Star Is Stable

Space physics

Lesson 2 of 4

Explain why a star stays the same size for billions of years.

1

Gravity

Pulls the star's matter inwards

2

Fusion

Hydrogen fuses to helium and releases energy, causing outward pressure

3

Balance

The forces balance so the star is stable

ANSWER

Inward gravitational force is balanced by outward thermal pressure.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Making the Elements

Space physics

Lesson 2 of 4

Explain how heavier elements are formed.

1

In stars

Nuclear fusion forms elements up to iron

2

In a supernova

The explosion has enough energy to form elements heavier than iron

3

Spread

The explosion scatters elements into space; new stars and planets form from them

ANSWER

Fusion makes elements up to iron; supernovae make heavier ones.

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Key Points

Space physics

Lesson 2 of 4

Learn these.

Main sequence

Hydrogen fuses to helium; stable for billions of years.

Red giant

Hydrogen runs out; the star expands and cools.

Supernova

A massive star explodes.

Black hole

An object with gravity so strong that not even light escapes.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Key Terms

Space physics

Lesson 2 of 4

Nebula

A cloud of dust and gas from which stars form.

Main sequence

The long stable stage of a star's life when hydrogen fuses to helium.

Red giant

A large, cool, red star near the end of its life.

White dwarf

A small, dense, hot star that is the core of a dead Sun-sized star.

Supernova

The explosion of a massive star at the end of its life.

Black hole

An object so dense that not even light can escape.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Space physics

Lesson 2 of 4

YOUR TASK

Star Story

12 minutes

Write the life story of the Sun and of a star ten times as massive. Where do they differ?

1

Mass controls the ending.

WHAT A GOOD ANSWER SHOWS

Sun: nebula, protostar, main sequence, red giant, white dwarf, black dwarf. Massive star: nebula, protostar, main sequence, red supergiant, supernova, neutron star or black hole.

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Can I...?

Space physics

Lesson 2 of 4

Describe a nebula.

Describe a protostar.

Explain stability.

Follow the Sun's path.

Follow a massive star's path.

Explain fusion and elements.

Define a supernova.

Define a black hole.

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Summary & Exam Focus

Stable when gravity and outward pressure are balanced.

Sun-sized: red giant, white dwarf, black dwarf.

Massive: red supergiant, supernova, neutron star or black hole.

Supernovae form elements heavier than iron.

EXAM FOCUS

Describe what happens to a star like the Sun when hydrogen runs out. (3 marks)

Red giant, white dwarf, black dwarf.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Life cycle of a star

Space physics

Lesson 2 of 4

Answer all questions. Use the mark allocation as a guide to how much to write. · 17 minutes

Question 1 · 2 marks · State

Name the stages in the life cycle of a star like our Sun after the main sequence.

Question 2 · 3 marks · Explain

Explain why a star on the main sequence is stable.

Question 3 · 4 marks · Describe

Describe the life cycle of a star that is much more massive than the Sun.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Exam Practice: Life cycle of a star (cont.)

Space physics

Lesson 2 of 4

Question 4 · 3 marks · Explain

Explain why some elements heavier than iron are found on Earth even though they cannot be made in the main sequence.

Question 5 · 4 marks · Explain

Explain how the Sun formed and why the Sun is stable.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 1 · 2 marks · State

Space physics

Lesson 2 of 4

“

Name the stages in the life cycle of a star like our Sun after the main sequence.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 1 · mark scheme

Space physics

Lesson 2 of 4

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

Red giant

1 mark

White dwarf

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 2 · 3 marks · Explain

Space physics

Lesson 2 of 4

“

Explain why a star on the main sequence is stable.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 2 · mark scheme

Space physics

Lesson 2 of 4

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

Gravity acts inwards

1 mark

Fusion energy gives outward pressure

1 mark

The forces balance

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 3 · 4 marks · Describe

Space physics

Lesson 2 of 4

“

Describe the life cycle of a star that is much more massive than the Sun.

HOW TO ANSWER IT

Command word: Describe. Worth 4 marks, so plan before writing.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 3 · mark scheme

Space physics

Lesson 2 of 4

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

Nebula / protostar / main sequence

1 mark

Red supergiant

1 mark

Supernova

1 mark

Neutron star or black hole

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 4 · 3 marks · Explain

Space physics

Lesson 2 of 4

“

Explain why some elements heavier than iron are found on Earth even though they cannot be made in the main sequence.

HOW TO ANSWER IT

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

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 4 · mark scheme

Space physics

Lesson 2 of 4

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

Supernova forms heavier elements

1 mark

Elements thrown into space

1 mark

Incorporated into new stars and planets

1 mark

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 5 · 4 marks · Explain

Space physics

Lesson 2 of 4

“

Explain how the Sun formed and why the Sun is stable.

HOW TO ANSWER IT

Command word: Explain. Worth 4 marks, so plan before writing.

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AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER

Question 5 · mark scheme

Space physics

Lesson 2 of 4

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

Gravity pulls dust and gas together

1 mark

Fusion begins

1 mark

Gravity acts inwards

1 mark

Balanced by outward pressure

1 mark

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