# Fields

## Fields

A field is a region in which a force is felt. These forces are non-contact forces.

There are a number of different fields such as gravitational, electric and magnetic.

Each field has their own properties but a number of them are similar in their description, behaviour and characteristics.

Gravitational and Electrostatic

Similarities and differences between Electric and Gravitational fields: You will often be asked to make these comparisons.

Gravitational fields

1. Vector quantity
2. Act on all particles with mass
3. Always attractive
4. F = mg where g = gravitational field intensity/strength (force per unit mass)
5. g is found by measuring the force exerted on a test mass of 1kg placed in the field
6. g measured in Nkg-1
7. Gravitational equipotentials are lines of equal gravitational energy

The forces between point masses obeys an inverse square law: ``````    There is nothing you can put round a mass to shield other masses from its gravitational effect.

Point masses and spherical masses produce a radial gravitational field directed towards the centre of the mass
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Electric fields

1. Vector quantity
2. Act on all particles with charge
3. Attractive and repulsive
4. F = qE where E = electric field intensity/strength (force per unit charge)
5. E is found by measuring the force exerted on a positive test charge (1C) charge
6. E is measured in NC-1
7. Electrical equipotentials are lines of equal electrical energy

The forces between point masses obeys an inverse square law: 1. A metal container connected to earth placed around a charge will shield other charges from its effect.

2. Point charges and spherical charges produce a radial electric field directed towards the centre of the negative charge and away from the centre of a positive charge