You are Here: Home >< A-levels

# Need help with A2 physics unit 4 multiple choice exam paper questions Watch

1. Hi,

Wondering if someone could explain to me & show the working required to get the correct answer to the following questions (correct is circled in red), from the AQA PHY4A 2010 & 2012 past papers

Questions: 4), 24), 14), 16) (see attachments)

Attachment 552674552676Attachment 552674552676552700
Attached Images

2. Bump, I would be very grateful if someone could help me out ASAP if they could, ask the exam is tommorrow, thanks.

Not sure if this is in the right section of the forum, but not sure how to move threads?
3. (Original post by JohnnyDavidson)
Bump, I would be very grateful if someone could help me out ASAP if they could, ask the exam is tommorrow, thanks.

Not sure if this is in the right section of the forum, but not sure how to move threads?
For the first one, the circumference of the earth is 1.5 x10^8 x 1000 x 2pi, and the time the earth takes to travel this distance is 365 x 24 x 60 x60. Then we're just using V = s/t to find the speed.
The second one, in order to induce an EMF in the secondary coil, there must be a change in the magnetic flux of the primary coil. The magnitude of this induced EMF is equal to the rate of this change, so when the switch is turned off suddenly the change is more rapid than when the current is building up initially, meaning the magnitude of the induced EMF is greater.
The last question, they're essentially asking you how kobg it takes for the voltage of the capacitor to drop to 90% of its original value. They tell you the initial current and voltage, so you can find the resistance and therefore
T = RCln0.9
Posted from TSR Mobile
4. (Original post by pineneedles)
For the first one, the circumference of the earth is 1.5 x10^8 x 1000 x 2pi, and the time the earth takes to travel this distance is 365 x 24 x 60 x60. Then we're just using V = s/t to find the speed.
The second one, in order to induce an EMF in the secondary coil, there must be a change in the magnetic flux of the primary coil. The magnitude of this induced EMF is equal to the rate of this change, so when the switch is turned off suddenly the change is more rapid than when the current is building up initially, meaning the magnitude of the induced EMF is greater.
The last question, they're essentially asking you how kobg it takes for the voltage of the capacitor to drop to 90% of its original value. They tell you the initial current and voltage, so you can find the resistance and therefore
T = RCln0.9
Posted from TSR Mobile
Hi, many thanks for explaining that, but I just have a few questions on your explanations for them.

24) (the second one) - but surely if the emf induced is maxed at this value, then induced current will be at its smallest value (from P = IV)?

14) also would you be able to explain this one, it's on the third page with 16) (I think you missed this one out)

Thanks
5. (Original post by JohnnyDavidson)
Hi, many thanks for explaining that, but I just have a few questions on your explanations for them.

24) (the second one) - but surely if the emf induced is maxed at this value, then induced current will be at its smallest value (from P = IV)?

14) also would you be able to explain this one, it's on the third page with 16) (I think you missed this one out)

Thanks
I don't think we assume that power is conserved in this situation, it would be V = IR, so a greater emf produces a greater current.
Yeah, I should have said, I'm not sure how to answer that one, so I'm sorry about that. I'm going to link you to a couple of threads for this exam, you could post it there and you will get more help.

http://www.thestudentroom.co.uk/show....php?t=4030039

http://www.thestudentroom.co.uk/show....php?t=4046575

Posted from TSR Mobile

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 19, 2016
Today on TSR

### Last-minute PS help

100s of personal statements examples here

### More pressure for kinky sex?

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.