6. Fields and Forces

Question 1

Outline Newton’s univesal law of gravitation

Answer 1

Every single point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversley proportional to the square of their separation

Question 2

Define gravitational field strength (g)

Answer 2

g = gives a measure of how much force a body will experience by a small test mass placed in a field g = F/m Unit: N kg-1

Question 3

What is the equation for the gravitational field around a spherical object?

Answer 3

F = G x (Mm) / r2

Question 4

What is the equation for addition of field?

Answer 4

g = (squared) g₁² + g₂²

Question 5

What 2 types of electric charge is there?

Answer 5

1. Positive 2. Negative

Question 6

State the law of conservation of charge

Answer 6

The charge can neither be created nor destroyed

Question 7

State Coloumb’s law

Answer 7

Couloumb’s law = The force experiences by two point charges is directly proportional to the product of their charge and inversely proportional to the square of their separation

k = 9 x 10⁹ Nm²C^-2

Question 8

Define electric field strength (E)

Answer 8

The electric field strength (E) =

• A measure of the force that a positive charge will experience if placed at a point in the field
• Defined as the force per unit charge experience by a small positive test charge placed in the field
• If a small positive charge q experience a force F in the field, then the field strength at that point is given by E = F / q

Question 9

Define magnetic flux density (B)

Answer 9

The strength of a fied is related to the density of field lines. This tells us that the magnetic field is strongest close to the poles.

The magnetic flux density = used to measure how strong the field is. Not the same as field strength used in gravitational and electric field.

Question 10

List three factors that size of the force is dependent on

Answer 10

1. How strong the field is - flux density (B)
2. How much current is flowing through the wire (I)
3. The length of the wire (l)

Question 11

What is the equation involving magnetc field of flux density, current, length and force?

Answer 11

**F = BIl **

F = Force

B = Magnetic flux

Current = I

Length = l