Physics homework help (GCSE P2) - induced charges

VioletPhillippo

Hi, I'm struggling with my homework on induced charges, I was wondering whether anyone could help? :smile:

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Reply 1

ronny98

Do you understand how electrostatic induction works? It's very simple once you know how...

Reply 2

VioletPhillippo

Original post by ronny98

Do you understand how electrostatic induction works? It's very simple once you know how...

We learnt about it in the lesson today & I can see it's a basic idea but for some reason it's confusing me :smile:

Reply 3

uberteknik

Original post by VioletPhillippo

We learnt about it in the lesson today & I can see it's a basic idea but for some reason it's confusing me :smile:

What exactly are you struggling with?

What are your thoughts on what's happening:

a) with the balloon?

b) with the water?

Reply 4

VioletPhillippo

Original post by uberteknik

What exactly are you struggling with?

What are your thoughts on what's happening:

a) with the balloon?

b) with the water?

Is the water moving towards the rod because the rod is positively charged & the water is negatively charged so they attract? It's the Q's about the water & the rod that I'm struggling to grasp at the moment :smile:

Reply 5

uberteknik

Original post by VioletPhillippo

OK, it's a little bit more complicated but you need to break down what is going on and then it's not so bad:

Atoms like to be balanced so that the number of protons = the number of electrons. In which case the opposite charges carried by the protons and electrons are also balanced and hence the charge forces cancel each other- rather like a tug of war where no side is winning - this is said to be charge neutral.

When there are less electrons than protons then the charge forces are imbalanced and the +ve proton charges are greater in number than the -ve electron charges. So the material has a net +ve charge force.

The opposite is true if there are more electrons than protons the -ve charges win out over the +ve and the material has a net -ve charge force.

That explains the charge on the rod: The atoms of the rod form a solid and whilst the protons in the nucleus are locked in position with relation to each other, the electrons are still free to be pulled off. Rubbing the rod caused some of the free electrons to be pulled off the surface and hence the rod has become net +ve charge.

Water molecules are also neutral charge. But unlike a solid, the molcules are free to move about.

At the same time, the electrons orbiting the atoms of the water molecule will sometimes be closer to the +ve charged rod than at other times. And because the force between charges gets stronger the closer together they are, those orbiting electrons will sometimes be closer to the rod on one side of theor orbit than on the other.

Think of it like the moon orbiting the earth will be closer to the sun than the earth during half of its orbit around the earth. Then for the other half of the orbit, it will be further from the sun than the earth. The net attractive force shifts with the orbit, greater when closer, less when further.

This slight imbalance of forces, together with the fact that in a liquid state, protons are not locked together like they are in a solid, the electrons atoms will try to move closer to the +ve charged rod and as they do so, they pull the whole water molecule with them.

(edited 9 years ago)

Reply 6

VioletPhillippo

Original post by uberteknik

OK, it's a little bit more complicated but you need to break down what is going on and then it's not so bad:

Atoms like to be balanced so that the number of protons = the number of electrons. In which case the opposite charges carried by the protons and electrons are also balanced and hence the charge forces cancel each other- rather like a tug of war where no side is winning - this is said to be charge neutral.

When there are less electrons than protons then the charge forces are imbalanced and the +ve proton charges are greater in number than the -ve electron charges. So the material has a net +ve charge force.

The opposite is true if there are more electrons than protons the -ve charges win out over the +ve and the material has a net -ve charge force.

That explains the charge on the rod: The atoms of the rod form a solid and whilst the protons in the nucleus are locked in position with relation to each other, the electrons are still free to be pulled off. Rubbing the rod caused some of the free electrons to be pulled off the surface and hence the rod has become net +ve charge.

Water molecules are also neutral charge. The electrons orbiting the atoms will sometimes be closer to the +ve charged rod than at other times. And because the force between charges gets stronger the coser together they are, the orbiting electrons will sometimes be closer to the rod than the proptons they are associated with.

This slight imbalance of forces, together with the fact that in a liquid state, protons are no locked together like thay are in a solid, the electrons atoms will try to move closer to the +ve charged rod.