GCSE physic help

When the switch is closed, the current has a new path of zero resistance that's through the switch and it will travel on that path instead of the 60ohm, so the total resistance goes down as the 60ohm resistor is no longer in play and because V=IR, I=V/R, so current increases when resistances decreases.

Reply 3

Rumi1380

10

because you closed the switch the current increase as it can flow through there now and therefore the total resistance decreases as it is a parallel circuit.
'As more and more resistors are added in parallel to a circuit, the equivalent resistance of the circuit decreases and the total current of the circuit increases. Adding more resistors in parallel is equivalent to providing more branches through which charge can flow'

Reply 4

OP

Original post by Radioactivedecay

When the switch is closed, the current has a new path of zero resistance that's through the switch and it will travel on that path instead of the 60ohm, so the total resistance goes down as the 60ohm resistor is no longer in play and because V=IR, I=V/R, so current increases when resistances decreases.

But can’t the current still flow through the 6ohm resistor, just not as much as before as there is a new zero resistance loop. Is that right?

Reply 5

OP

Original post by Mathematics Man

Do you understand why the resistance decreases?

No I don’t get that bit

Reply 6

Mehru1214

Original post by Defence11

Hello guys.. It would be great if u helped me. I don’t understand this physics exam question. http://filestore.aqa.org.uk/resources/physics/AQA-84631H-SQP.PDF That is the link for the paper. The question is 7.3. I do not understand what the mark scheme says what why it is the answer. It would be much appreciated if u answered. Thanks http://filestore.aqa.org.uk/resources/physics/AQA-84631H-SMS.PDF That is link to mark scheme. Thanks

When the switch is closed, the 60 ohm resistor is short-circuited, so current doesn't flow through it, only through the switch's wire. So the total resistance decreases due to one resistor being out of action.

By Ohm's Law, V = IR.

The voltage remains constant, and dividing it by a smaller value of R results in the current, I, increasing.

Hopefully that made sense!

Reply 7

OP

Original post by Mehru1214

When the switch is closed, the 60 ohm resistor is short-circuited, so current doesn't flow through it, only through the switch's wire. So the total resistance decreases due to one resistor being out of action.

By Ohm's Law, V = IR.

The voltage remains constant, and dividing it by a smaller value of R results in the current, I, increasing.

Hopefully that made sense!

Last bit does but the first bit doesn’t. I still would have thought current would flow through the 60ohm resistor but just not as much as before. Am I right. Or is there no current flowing through the 60ohm resistor when the switch is closed

Reply 8

Mehru1214

Original post by Defence11

Last bit does but the first bit doesn’t. I still would have thought current would flow through the 60ohm resistor but just not as much as before. Am I right. Or is there no current flowing through the 60ohm resistor when the switch is closed

No current flows through resistor when switch is closed, the whole route is bypassed due to the switch.

Reply 9

OP

Original post by Mehru1214

No current flows through resistor when switch is closed, the whole route is bypassed due to the switch.

But that Doesnt make sense cause normally in a circuit let’s say a voltmeter is connected in parallel to a lamp. Current flows through the lamp and voltmeter right?

Reply 10

Radioactivedecay

Original post by Defence11

But that Doesnt make sense cause normally in a circuit let’s say a voltmeter is connected in parallel to a lamp. Current flows through the lamp and voltmeter right?

This is a different case. When the current has of choice of going through one of two paths, one with zero resistance and another with non zero resistance, all of it will always go through the path with zero resistance, that's just a property of current. It can be shown mathematically, but it's not need for GCSE level.

Reply 11

OP

Original post by Radioactivedecay

This is a different case. When the current has of choice of going through one of two paths, one with zero resistance and another with non zero resistance, all of it will always go through the path with zero resistance, that's just a property of current. It can be shown mathematically, but it's not need for GCSE level.

As this was in the GCSE paper how was I supposed to know that current will always pick the zero resistance path. Now I know thanks to you but seriously don’t u think that was hard because not many students would pick up on that theory

Reply 12

OP

Original post by Radioactivedecay

This is a different case. When the current has of choice of going through one of two paths, one with zero resistance and another with non zero resistance, all of it will always go through the path with zero resistance, that's just a property of current. It can be shown mathematically, but it's not need for GCSE level.

Why is it in a gcse paper then

Reply 13

SlashaRussia

15

Original post by Defence11

Why is it in a gcse paper then

It's GCSE level knowledge, its just that there is a mathematical way to show this also which you don't need (for this level). For GCSE you just need to be able to explain it with words, that's what it means.

Reply 14

Anonymouspsych

Original post by Defence11

Hello guys.. It would be great if u helped me. I don’t understand this physics exam question. http://filestore.aqa.org.uk/resources/physics/AQA-84631H-SQP.PDF That is the link for the paper. The question is 7.3. I do not understand what the mark scheme says what why it is the answer. It would be much appreciated if u answered. Thanks http://filestore.aqa.org.uk/resources/physics/AQA-84631H-SMS.PDF That is link to mark scheme. Thanks

As soon as the switch is closed, the current won't flow through the 60 ohm resistor anymore because there is a new path of no resistance which the current prefers to take.

In a series circuit (which this is), the total resistance of the circuit is the sum of the individual resistances of the resistors. So this means as soon as the switch is closed, the 60 ohm resistor can be excluded and so your new total resistance is smaller by 60 ohms.

Using Ohm's law V=IR and hence I=V/R . We know V is fixed as the supplied voltage is 12 V but because the resistance is now smaller this means the current will now increase.

Reply 15

OP

Wh

Original post by Anonymouspsych

As soon as the switch is closed, the current won't flow through the 60 ohm resistor anymore because there is a new path of no resistance which the current prefers to take.

In a series circuit (which this is), the total resistance of the circuit is the sum of the individual resistances of the resistors. So this means as soon as the switch is closed, the 60 ohm resistor can be excluded and so your new total resistance is smaller by 60 ohms.

Using Ohm's law V=IR and hence I=V/R . We know V is fixed as the supplied voltage is 12 V but because the resistance is now smaller this means the current will now increase.

Why does the current prefer to take the path with no resistance? In my cgp book it doesn’t say that anywhere

Reply 16

OP

Original post by SlashaRussia

It's GCSE level knowledge, its just that there is a mathematical way to show this also which you don't need (for this level). For GCSE you just need to be able to explain it with words, that's what it means.

Why does the current prefer to take the path with no resistance? In my cgp book it doesn’t say that anywhere

Reply 17

Anonymouspsych

Original post by Defence11

Wh

Why does the current prefer to take the path with no resistance? In my cgp book it doesn’t say that anywhere

The current cannot take both paths as there will be a potential difference across the 60 ohm resistor but no potential difference across the 0 resistance path. This means the when the electrons meet at the 2nd junction they wont have the same amount of energy and this isn't allowed.

Hence it must take either take the 60ohm resistance path or the no resistance path. It just so happens to be the electrons always take the path of 0 resistance. There are mathematical explanations for this but you don't need to worry about that!

Reply 18

OP

Original post by Anonymouspsych

The current cannot take both paths as there will be a potential difference across the 60 ohm resistor but no potential difference across the 0 resistance path. This means the when the electrons meet at the 2nd junction they wont have the same amount of energy and this isn't allowed.

Hence it must take either take the 60ohm resistance path or the no resistance path. It just so happens to be the electrons always take the path of 0 resistance. There are mathematical explanations for this but you don't need to worry about that!

Can’t it take both

As in this example it flows through the voltmeter and lamp

Reply 19

Anonymouspsych