Electric fields

All knowledge and terms for AQA A-level Electric Fields topic.

If a system has positive EPE, what happens?

If a system has positive EPE, what happens?

System is unstable, charges repel.

If a system has negative EPE, what happens?

System is stable, charges attract.

What experiences electric fields?

An object with charge.

Direction of field lines for a positive source?

Away from the source.

Direction of field lines for a negative source?

Towards the source.

What is the electric potential energy store?

The store available to a charge in an electrostatic field. Where energy is transferred to/from due to work done by the electrostatic force.

Change in the electric potential energy = ?

= work done by electrostatic force.

Unit for field strength vector for the electrostatic force.

Joules per unit charge.

What is the electrostatic potential?

The work done per unit charge on a positive test charge when it is moved from infinity to that point in space. (joules/coulomb)

Values for potential if source is positive?

positive

Values for potential if source is negative?

negative

Total potential = ?

Sum of individual potentials at that point.

Equation relating potential, work done and charge.

V = W/q

Equation relating potential, electric potential energy and charge.

V = E/q

What does a drop in the potential indicate?

An expenditure of energy.

What is an equipotential?

Lines which connect points of all equal potentials. Spherical charges have spherical equipotentials. They are perpendicular to the field lines of a source.

What happens to a negatively charged particle when the potential is increasing.

• V>0

• particles lose electric potential energy, Ep<0

• The field accelerates the particle, increasing its kinetic energy

• Particle moves from low to high potential

• Work done by the field is positive.

What happens to a positively charged particle when the potential is decreasing.

• V<0

• particle loses electric potential energy, Ep<0

• Field accelerates the particle, increasing its kinetic energy

• Particle moves from high to low potential

• Work done by the field is negative.

What is the work done by the electric field on a positive particle with increasing potential.

negative work done

What is the work done by the electric field on a negative particle with decreasing potential.

positive work done

Define electric field strength

Force per unit of charge on a positively charged particle.

units for electric field strength.

volt per metre = Vm^-1