Electric field strength (A-level only) Flashcards – AQA A-level Physics (7408)

What direction does an electric field line indicate at a point?

The direction of the force on a positive test charge at that point.

Which way do electric field lines point relative to positive and negative charges?

Away from positive charges and towards negative charges.

How do electric field lines represent relative field strength?

A greater density of lines represents a stronger field.

Why can electric field lines not cross?

The electric field has a single direction at each point.

How is a uniform electric field represented by field lines?

By parallel, equally spaced lines.

What is the shape of the electric field lines around a point charge?

They radiate outwards or inwards.

What is the electric field strength between parallel plates in a uniform field, in terms of the potential difference $V$ and plate separation $d$?

$E = \frac{V}{d}$

For a charge of magnitude $Q$ moving a distance $d$ between plates through a potential difference of magnitude $\Delta V$, how are the magnitudes of work done by the electric force and electrical energy change related?

$Fd = Q\Delta V$

What is the magnitude of the electric force on a charge of magnitude $Q$ in an electric field of strength $E$?

$F = QE$

How does electric field strength vary within a uniform electric field?

It is constant.

In which direction does an electric field point relative to electric potential?

Towards decreasing electric potential.

What is the magnitude of the electric force on a particle of charge $q$ in an electric field of magnitude $E$?

$F = |q|E$

How does a charged particle accelerate in a uniform electric field, and how does the direction depend on its charge?

Its acceleration is constant: along the field for a positive charge and opposite the field for a negative charge.

A charged particle enters a uniform electric field with velocity perpendicular to the field. How do its velocity components change while it is in the field?

The perpendicular component remains constant; the parallel component changes uniformly.

What path does a charged particle follow inside a uniform electric field if it enters perpendicular to the field and other forces are negligible?

A parabolic path.

What is the electric field-strength magnitude at distance $r$ from an isolated point charge of magnitude $|Q|$?

$E = \frac{1}{4\pi\varepsilon_0}\frac{|Q|}{r^2}$

$\varepsilon_0$ is the permittivity of free space.

What is the direction of the electric field around a positive or negative point charge?

Positive charge: radially outward.
Negative charge: radially inward.