A non-contact force acts through a region of space called a force field. When you drop an object, it is pulled towards the Earth due to the Earth’s gravitational force field. A balloon can be charged and attract a tub of nails if they lie within its magnetic field. Powerful electromagnets can lift heavy steel.

Magnetic fields

A magnet pulls, or attracts, materials containing the metals iron, cobalt or nickel. Steel is made from iron, and so steel is also attracted to a magnet. A horseshoe magnet can attract steel filings from a distance away.

A magnetic field is a space around a magnet where a magnetic force is experienced. The steel filings were pulled by a magnetic force in the direction of the magnetic field.

The ends of a magnet are called poles. If a magnet floats in water, then one end spins to face the earth’s north pole of the magnet. The opposite pole of the magnet is the south pole. If a magnet is cut in half each half still has a north and a south pole. The magnetic field is strongest at the poles of the magnet.

A magnetic field is normally invisible to us. Its shape and strength can be determined either by passing a compass around a magnet, or by examining a sprinkling of iron filings around a magnet.

Magnetic field lines:

• Show the direction that a compass would point
• always run from the north pole to the south pole
• do not cross
• represent a strong magnetic field when they are bunched closely together.
• represent a weak magnetic field when they are spaced further apart.

Attraction and repulsion of poles

In science:

• Opposites attract

This means that North-South charges are attracted to each other. Whereas North-North and South-South repel each other.

Magnetic domains

The only metals that are attracted to magnets are IRON, NICKEL AND COBALT. This means that all other substances are not.

Scientists believe that inside each of these metals are tiny magnetic particles called domains. Each of these acts like a mini-magnet, and has a north and south pole. In a piece of magnetized iron, the domains all point in the same direction. This means that the metal acts like a magnet. The domains in a piece of unmagnetised iron point in random directions.

Kahoot?

Electric fields

Force fields also exist around electric charges. To understand electric fields, you first need to understand the atom and its internal structure.

What is an atom?

Everything around us is made up of tiny particles called atoms. Atoms are made up of even smaller particles called protons(+) neutrons(0) and electrons(-).

Protons and Neutrons are found within the deepest part of the atom know as the nucleus. Electrons move around the space around the nucleus (like how the moon moves around earth).

Unit review 7.4 Part 1
Homework:

• Answer questions 1-4 and 9 here:

  In here: 1.

1. a) non – contact force ✅

b) increases ✅

c) south pole ✅

d) strongest ✅

2. 1. Whiteboard magnets ✅

3. fridge magnets ✅

4. speakers ✅

5. headphones ✅

6. laptop speakers ✅

7. Iron, Nickel and Cobalt ✅

8. a) protons

b) electrons

9. a) attract

b) attract

c) repel ( sorry I am kind of confused on this) (attract)

d) repel

• Let’s talk about North-South pole interactions and Positive and negative interactions. (repelling and attracting)

Charging up ⚡️ 🔌

Normally a material has no charge, this is because the number of protons and electrons are balanced. If one material is rubbed against another, electrons may move from one substance onto the other. If this happens, the number of protons and electrons is no longer balanced.

Some materials, such as plastic, rubber and wood, will build up charge when rubbed with another substance. Such materials are called electrical insulators. Electrons cannot flow freely through them. The reason electrical wires are covered with plastic is because plastic is an effective electrical insulator.

Metallic objects do not build up a static charge, because electrons can flow through them. These materials, such as copper electrical wire, are called electrical conductors.

Simply put, conductors let electricity pass through them, these are usually metals, and insulators stop electricity from flowing through them, things like

Questions

1. What kinds of materials around the house do you think conduct electricity?
2. What kinds of materials around the house do you think insulate electricity?

When a glass rod is rubbed with a silk cloth, electrons move from the glass rod onto the silk cloth. The glass rod has lost electrons and now is positively charged, because it has more protons than electrons. the silk cloth has gained electrons and is negatively charged, having more electrons than protons. The silk cloth has gained electrons and is negatively charged, having more electrons than protons. When an object becomes charged, it has unequal numbers of protons and electrons, we say that is has static electricity.

A Force field called an electric field exists around any object that is charged. Any charged object positioned within this field will experience a force, called an electrostatic force (or an electric force).

If you rub a balloon with a silk cloth, electrons rub off the silk and onto the balloon. Both the silk cloth and the balloon are now charged, and are surrounded by an electric field. The image below shows what happens when these charged objects are placed next to each other. If placed inside an electric field, two objects with different types of charges will attract each other, while those with the same type of charge will repel. Note that the changed object may also attract a neutral object.

A machine called a Van de Graaff generator separates charge by friction between a moving rubber belt and a plastic pulley. Negative charges are released to flow through to the ground, while positive charges are transferred onto the dome of the generator. The girl touching the dome of the generator in this image becomes positively charged. Her hair stands up because each strand of hair is repelling the hair around it!

Static discharge

Static electricity describes a build-up of charge. If you walk across carpet on a dry day and touch a metal door handle, you could get a shock. Friction between your feet and the carpet rub electrons from the carpet onto you, making you and the carpet both charged. Normally, this charge gradually leaks back out of your shoes to the ground, or into the air, and you become neutral once more. If there is a big build-up of charge, or if you wear rubber-soled shoes that stop the charge from escaping, extra electrons can jump from you to the metal door handle as a spark. You feel this as a small electric shock. If you were to touch another person while charged, electrons would jump onto this person and you would both feel a static shock.

Homework/Class activities
7.4 Part 2