Electriticy

Question 1

When charging a cell, where is the positive terminal of the battery AND WHY

Answer 1

positive terminal is always next to the positive terminal of the cell (big line)

Reason is because current direction had to be reversed so that energy is transferred to the cell

Explanation
- because if it was other way, then current is going from cell to circuit, and so energy is being transferred away from cell. But since energy must be transferred TO the cell, current direction had to be reversed ( and conventional current goes from POSITIVE TERMINAL TO NEGATIVE, hence positive part of battery connects to positive part of the cell terminal )

And similar thing happens in capacitor when cell charges it, positive and positive meet !!!

Question 2

What are limitations of the resitivity practical, why is final value different 3

Answer 2

1) heating in the wire means the reistance increases , so higher value for resitivity
2) ammeter voltmeter don’t show proper values due RESITANCE in ammeter , and not enough in volts showing less current and so higher reistance and thus resitivity
3) increased reistance due to crocodile clips

Question 3

How to find total number of electrons per second?

Answer 3

The total charge = number x e
So find charge in one second, current , and divide by e (or whatever the charge is)

Question 4

When doing a sensing circuit, waht reidtor do we chose if we want the largest scale change on thr resding and why?

Answer 4

largest scale change means high differences in voltage, because that’s what it reads
# therefore you want the change in light intensity ti reflect the biggest percentage of resistance to increase voltage in potential divider
- so you choose the LOWEST RESITIR, and hence your change will give rise to the highest percentage , and so highest voltage and so highest reading

Question 5

Remember RESISTANCE ON A GRAPH is not equal to eben INSTANTANEOUS gradient!, so how to find it at different points on the graph.

Answer 5

Must just say R= V/I
At any point, read thr V value and the I value amd perform the calculation

Referring to GRADIENT IS INCORRECT

Question 6

Why are extra fixed resistors used in circuits?

Answer 6

This LIMITS THE CURRENT IN TJE CIRCUIT, ensuring the LED doesn’t burn out

Question 7

How to say why potntial divider with slider is better than variable reisotr

Answer 7

Say potential divider cna give full range of v, and show WHY THE VARIABLE RESISIOR can’t

• do this by subbing in max , and this gives min, and subbing in 0, and this should give full
• you should find you can get max voltage but can’t get smaller values, no matter what

Mention that because there will always be some voltsge through variable resistor, csn’t ever get this to be max voltage going through, for the other part to be 0 volts

Question 8

How to link current and photons ideas togther in this q

Answer 8

Remember find the electrons needed, thus photons, thus energy…