Practise Electric fields. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
The dome of a Van de Graaff generator becomes positively charged. An earthed metal sphere is slowly moved towards the dome. When the sphere is close enough, a spark jumps across the gap. State the direction in which electrons flow in the spark.
From the earthed sphere to the (positive) dome.
A small, negatively charged plastic sphere hangs from an insulating thread. A positively charged rod is brought near to the sphere but does not touch it. Describe what happens to the sphere.
It moves towards the rod (the thread swings towards the rod).
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy2 marks
(a) An isolated charged sphere has an electric field around it. What happens to the electric field strength as you move further from the sphere? Tick (✓) one box.[1]
It increases.
It decreases.
It stays the same.
(b) What is used to represent an electric field in a diagram?[1]
Show the answer and mark scheme
(a)Answer: It decreases.
(b)Answer: Field lines
field lines
Question 2Medium6 marks
A small, negatively charged plastic sphere hangs from an insulating thread. A positively charged rod is brought near to the sphere but does not touch it.
(a) Describe what happens to the sphere.[1]
(b) Explain, using the idea of an electric field, why the sphere moves even though the rod does not touch it.[2]
(c) The rod is moved closer to the sphere. Describe and explain how the angle between the thread and the vertical changes.[2]
(d) The positively charged rod is replaced by a negatively charged rod. Describe what happens to the sphere.[1]
Show the answer and mark scheme
(a)Answer: It moves towards the rod (the thread swings towards the rod).
it moves / swings towards the rod
(b)Answer: The charged rod creates an electric field around itself; the charged sphere is in this field, so it experiences a (non-contact) force.
the (charged) rod creates an electric field around it
the (charged) sphere is in the field so it experiences a force
(c)Answer: The angle increases, because the electric field is stronger closer to the rod, so the force on the sphere is greater.
the angle increases
the field is stronger closer to the rod so the force (of attraction) on the sphere is greater
(d)Answer: It moves away from the rod (it is repelled).
it moves / swings away from the rod / is repelled
Question 3Hard6 marks
The dome of a Van de Graaff generator becomes positively charged. An earthed metal sphere is slowly moved towards the dome. When the sphere is close enough, a spark jumps across the gap.
(a) Explain, in terms of the electric field, why the spark only jumps when the sphere is close enough to the dome.[3]
(b) State the direction in which electrons flow in the spark.[1]
(c) A student standing on an insulating mat touches the dome. The student's hairs stand on end. Explain why, using the idea of electric fields.[2]
Show the answer and mark scheme
(a)Answer: The electric field is strongest close to the charged dome and gets stronger between the dome and sphere as the gap decreases; when it is strong enough, the air becomes ionised (conducts) and charge flows as a spark.
the electric field is strongest close to the (charged) dome
as the gap decreases, the field between the dome and the sphere gets stronger
when the field is strong enough the air is ionised / becomes a conductor, so charge flows / a spark jumps
(b)Answer: From the earthed sphere to the (positive) dome.
from the (earthed) sphere to the dome
(c)Answer: Each hair gains the same type of charge; each hair is in the electric field of the others, so it experiences a repulsive force and the hairs move apart.
each hair has the same type of charge (positive)
each hair is in the electric field of the others / of the charged student, so it experiences a force repelling it from the others