Fields (A-level only) Flashcards – AQA A-level Physics (7408)

What is a force field?

A region where a body experiences a non-contact force through interaction with a source.

What gives rise to gravitational fields, electrostatic fields and magnetic forces, respectively?

• Gravitational fields: mass
• Electrostatic fields: static charge
• Magnetic forces: interactions between moving charges

How can a force field be represented at each point?

By a vector with a magnitude and direction.

How is the direction of the force on a body determined from a field?

It depends on the field and the nature of the interaction; it is not necessarily the field direction.

How do gravitational and electrostatic force magnitudes between point sources depend on their separation $r$?

Both are proportional to $1/r^2$.

How do gravitational and electrostatic forces differ in whether they attract or repel?

Gravity between masses is always attractive. Electrostatic force attracts unlike charges and repels like charges.

What does the direction of a field line indicate at a point?

The field direction at that point.

What does field-line density indicate?

Relative field strength.

How are gravitational and electric field directions defined using test bodies?

Gravitational field direction is the direction of force on a test mass; electric field direction is the direction of force on a positive test charge.

How are gravitational potential and electric potential defined?

Gravitational potential is potential energy per unit mass; electric potential is potential energy per unit charge.

What is an equipotential surface?

A surface joining points at the same potential.

How much work does a field do when a test body moves along an equipotential surface?

No work.

How are field lines oriented relative to equipotential surfaces?

They are perpendicular to the surfaces.