Edexcel IGCSE Physics- Static electricity

How can we charge insulators?

- By rubbing them together as long as they are made from different materials. (friction)

- Rubbing objects together removes the electromagnetic forces of attraction.

- electrons are transferred from one object to the other

- One becomes positively charged and the other negatively charged

- The object that gains / loses electrons depends on the material

Insulators

Do not conduct electricity:

- Electrons cannot flow throughout the material

- Fixed electrons

Conductors

Conduct electricity because their electrons

- Can FLOW

- Are DELOCALISED

i.e: Metals, graphite

Practical: investigate how insulating materials can be charged by friction

Suspend one of the insulating materials using a cradle and a length of string so that the material can rotate freely.

Rub one end of the material using a cloth (in order to give it a charge).

Now take a second piece of insulating material and charge that by rubbing with a cloth.

Hold the charged end of the second piece close to the charged end of the first piece:

If the first piece rotates away (is repelled) from the second piece then the materials have the same charge.

If the first piece moves towards (is attracted to) the second piece then they have opposite charges.

Explain how positive and negative electrostatic charges are produced on materials by the loss and gain of electrons

If an atom gains extra electrons, it will gain an overall negative charge.

If it loses some of its electrons it will be left with a positive charge.

What are the forces between like and unlike charges

Force of attraction between unlike charges

Forces of repelling between like charges

Explain electrostatic phenomena in terms of the movement of electrons

When two objects are rubbed together:

One of them will gain electrons and hence gain a negative charge.

The other will lose electrons and hence gain a positive charge.

How can static electricity be used for insecticides/spray paint

The nozzle gives the paint particles a negative charge because of the FRICTION between particles and the (air resistance)

- The object you are spraying is given a positive charge.

- This attracts the paint particles to the object being sprayed

- It gives it an even spread because the particles repel from each other. (same charge)

What would happen if droplets were not charged?

- Will blow away

- droplets will be spread unevenly

Electrostatic forces

- A non-contact force of electric charges at rest.

Greater charge = greater force

Closer together = greater force

- Force is proportional to the inverse square of distance

When does sparking occur?

- Occurs when enough charge builds up and the objects are close but not touching

What is the spark?

- When the charge JUMPS through the air from the highly positive object to the highly negative to balance out the charges

Lightning

Occurs when the difference between the earth and the ground is so large a massive spark jumps across to balance the charges

Explain the potential dangers of electrostatic charges, e.g. when fuelling aircraft and tankers

When a plane is refuelled, the fuel has to be pumped at a fast rate.

Friction between the fuel (a liquid insulator) and the pipe causes the fuel to gain a charge.

If this charge were to cause a spark the fuel could ignite.

To prevent this, planes are connected to the earth with a copper wire (the bonding line) whilst they are being refuelled.

This wire removes charge from the plane by carrying it to the earth, which removes the risk of any sparks.

How to prevent sparking

EARTHING

Planes are connected to the earth with a copper wire (the bonding line) whilst they are being refuelled.

This wire removes charge from the plane by carrying it to the earth, which removes the risk of any sparks.

inkject printer

-tiny droplets of ink are forced out of fien nozzel, making them eectrically charged

-two plates have voltage applied to them make them positive/ negative

- this controls the path of the ink droplet

photcopier

1. An image of the document is projected onto a positively charged copying plate

2. The plate loses its charge in the light areas and keeps the positive charge in the dark areas (i.e the text)

3. A negatively charged black toner powder (the ink) is applied to the plate and sticks to the part where there is a positive charge

4. The toner is then transferred onto a new blank sheet of white paper

5. The paper is heated to make sure the powder sticks (hence why photocopied paper feels warm)