# AQA A-Level Physics question: Electric fieldsWatch

#1
I need help with part b) of the following question:

An insulated metal conductor is earthed before a negatively charged object is brought near it.

a) Explain why the free electrons move as far away from the charged object as they can.

b) The conductor is then briefly earthed. The charged object is then removed from the vicinity of the conductor. Explain why the conductor is left with an overall positive charge.

I understand that in part a) the delocalised electrons in the metal are negatively charged so they are repelled by the object but could someone please explain the theory of part b) to me? Many thanks.
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11 months ago
#2
I need help with part b) of the following question:

An insulated metal conductor is earthed before a negatively charged object is brought near it.

a) Explain why the free electrons move as far away from the charged object as they can.

b) The conductor is then briefly earthed. The charged object is then removed from the vicinity of the conductor. Explain why the conductor is left with an overall positive charge.

I understand that in part a) the delocalised electrons in the metal are negatively charged so they are repelled by the object but could someone please explain the theory of part b) to me? Many thanks.

The following video describes the induction process that you are looking for.

When the conductor is earthed, the electrons will flow to the Earth via the earthing connection, leaving the induced positive charges in the conductor.
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#3
(Original post by Eimmanuel)
The following video describes the induction process that you are looking for.

When the conductor is earthed, the electrons will flow to the Earth via the earthing connection, leaving the induced positive charges in the conductor.
Thanks I understand charging by induction now. Just one quick question when the conductor is left with an overall positive charge and the negatively charged object is taken away won't the conductor then be discharged by the earth though as the electrons are attracted back to the positive ions in the metal conductor due to the absence of the object?
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11 months ago
#4
Thanks I understand charging by induction now. Just one quick question when the conductor is left with an overall positive charge and the negatively charged object is taken away won't the conductor then be discharged by the earth though as the electrons are attracted back to the positive ions in the metal conductor due to the absence of the object?
If you watch the video again, the earth connection to the conductor is removed before the negatively charged object is removed to ensure that the conductor is positively charged.
However, if the negatively charged object is removed before the earth connection is disconnected, the conductor indeed will be neutral, which is explained by you.
...the conductor then be discharged by the earth though as the electrons are attracted back to the positive ions in the metal conductor...
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