From Textbook Summary Qs

Question 1

Calculate the charge passing a point in x seconds with current xAmps

Answer 1

Use Q=IT

Coulomb is unit o charge,Q

Question 2

Calculate the average current in a wire through which a charge of 15C passes in 5s

Answer 2

Use Q=IT

Question 3

Calculate the number of electrons passing a point in the wire in 10 minutes when the current in 5.0 amps

Answer 3

Use Q=IT for the charge

Charge / (1.6x10-19) for number of electrons

Question 4

A certain type of rechargeable battery is capable of delivering a current of 0.2A for 4000s before its voltage drops and it needs to be recharged. Calculate the max time it could be used for if the current through it was 0.5 amps

Answer 4

Use q=It for the max charge

Sub into equation 0.5amps X t =(maxQ)

Solve for t

Question 5

Explain why sampling data from a computer and sensor is a sensible option

Answer 5

Readings need to be taken more quickly than could be achieved by manual thinking

Question 6

Suggest a suitable sampling rate for such an experiment, giving a reason for your answer

(Current- time graph of a 12V filament lamp)

Answer 6

Rate : more than 40 times per second

Reason

The current rises very rapidly for the first 0.1 seconds and you should have 4 results for this section of the graph

Question 7

Explain why the current rises to a high value before falling to a steady value

And

Why a filament is more likely to fail when being switched on than at other times

6 marks

Answer 7

Initial R is low- initial A is high// the temp is low then is high

The temp heats up, increasing resistance - which causes current to fall

Current is steady when energy supplied = energy lost from filament –or when temp is constant

Max heating is produced from the start when the current is at its max

Melting of filament cause fail- could be a mechanical failure caused by temp rise

When switched on energy is supplied more rapidly than it is lost so filament melts

Question 8

What is a super conductor?

Answer 8

Sketch the graph
          ///////
          |
          |
------|

Y is resistivity
X is temperature

0 resistivity at and below the critical temp

Question 9

Explain why superconductors are useful for applications which require very large electric currents and name two such applications

Answer 9

When resistance is zero there is no energy lost

Power cables, electromagnets, motors, fusion reactors, MRI scanners, monorail trains, fusion reactors, particle accelerators

A superconductor is only really useful if less energy is used to maintain the ;generally low) transition temp of the substance than is saved by the super conductor