Lesson 1 - Electric charges and fields

Electric field, positive charge, attract, repel

Electric field, positive charge, attract, repel

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Electric field, positive charge, attract, repel

Title: P4, Lesson 1

Electrical charges and fields

Learning objectives

• Describe how insulating materials can become charged.�
• Explain the interactions between charged objects with respect to their electric field.�
• Explain why static shocks occur.

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• Explain how a Van de Graaff generator works.

Electric field, positive charge, attract, repel

A quick reminder...

• The nucleus of an atom has a positive charge.�
• The electrons of an atom have a negative charge.�
• Removing electrons from an uncharged atom makes it positive.�
• Adding electrons to an uncharged atom makes it negative.

Electron

Electric field, positive charge, attract, repel

Charging by friction

• If you rub an insulating material with a dry cloth, electrons will either be transferred onto the cloth from the rod, or onto the rod from the cloth.�
• This only works for insulating materials, why?

Electric field, positive charge, attract, repel

Charging by friction

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• If two rods of the same material are rubbed with the same type of cloth, they gain the same type of charge. What do objects with the same charge do to each other?�
• What do objects with opposite charges do to each other?

Electric field, positive charge, attract, repel

Key points

• Like charges are repelled.�
• Opposite charges attract.

Electric field, positive charge, attract, repel

Electric fields

• The attractive or repulsive �forces between charged objects �is caused by an electric field �that forms around charged �objects.�
• The field lines are lines of force that charged particles can move along.�
• Arrows on lines of force move away from positively charged objects and towards negatively charged objects.

Electric field, positive charge, attract, repel

Task

• Draw the electric field lines around:�
• A positively charged sphere�
• A negatively charged sphere�
• How does the strength of the force change as objects move apart from each other?

Electric field, positive charge, attract, repel

The size of the force decreases as the charged objects are moved apart.

Electric field, positive charge, attract, repel

Static shock - sparks

• As the distance between two charged objects decreases, the force between them increases.
• As the force gets stronger, it draws electrons in air molecules towards the positive charge.
• This causes a stream of electrons to flow from the negatively charged object to the positively charged object.
• The air gets so hot it glows white, this is what you see as the spark

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Static electricity Phet simulation

Electric field, positive charge, attract, repel

Van de Graaff generator - watch the video

Electric field, positive charge, attract, repel

• The spinning belt removes electrons from the metal sphere, leaving it positively charged.

Electric field, positive charge, attract, repel

Task - Answer in full sentences:

Explain why a person’s hair will stand on end when they touch the Van de Graaff generator.

Electric field, positive charge, attract, repel

Why does the Van de Graaff generator make hair stand up?

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• Electrons are drawn off the person.
• This gives them a positive charge.
• The positive charge on the head repels the positive charge on the hair, making them stand up.
• The positive charges on the hair repel each other.

Electric field, positive charge, attract, repel

Task

Complete the exam question or BBC Bitesize quiz

Electric field, positive charge, attract, repel