Chapter 2

Question 0

Current, I =

3

Answer 0

1) charge/time
Q/t
2) number of ions arriving per second x charge on ion
Nq
3) electron density x charge on 1 electron x average drift velocity x area
nevA

Question 1

Potential difference

Answer 1

Made by uneven distribution of charge. Difference in potential energy of a charge going between those places, per unit charge. Anywhere there is a change in energy V, volts V

Question 2

Potential difference, V =

Answer 2

Energy/charge

E/Q

Question 3

Power

Answer 3

Rate of delivery of energy, P, watt W

Question 4

Current

Answer 4

Rate of flow of charge, Q, amperes A

Question 5

Power =

4

Answer 5

1) IV (current x p.d.)
2) I^2 R (using V=IR)
3) V^2/R (using I=V/R
4) E/t (energy over time)

Question 6

Charge on an electron/singly charged ion (magnitude)

Answer 6

1.6x10^-19 C, e

Question 7

Conductance, G =

Answer 7

current/potential difference

I/V

Question 8

Conductance

Answer 8

Measure of how much currency flows for a given p.d. G, Siemens S

Question 9

Resistance

Answer 9

How badly things conduct. NOT fighting back! Lack charge carriers which can move. How much current is lost in a circuit. Takes energy away from electrons. R, ohms

Question 10

Resistance, R =

2

Answer 10

1) p.d./current (V/I)

2) 1/conductance (1/G)

Question 11

Ohm’s law

Answer 11

Relates current through a conductor to p.d. States current is proportional to p.d. providing other physical conditions remain constant (e.g. heat).

Question 12

Series circuits

Answer 12

• current is constant

* Rt = R(1) + R(2)

Question 13

EMF

Answer 13

Stands for electromotive force - misnomer! Where electrons gain potential difference (in the source). Energy given to each unit charge - not all in circuit due to internal resistance!

Question 14

Kilowatt hour

Answer 14

1000W for 1hr.
1000Js^-1 for 1hr
1000Js^-1 for (60 x 60)
1000Js^-1 for 3600s
3.6MJ

Question 15

Parallel circuits

Answer 15

• 1/Rt = 1/R(1) + 1/R(2)

* p.d is the same across each branch

Question 16

EMF (funny E) =

Answer 16

1) V(R) + V(r)
2) I(R + r) –> deduced using V=IR
3) electrical potential energy gained in other forms/unit charged

Question 17

Terminal potential difference

Answer 17

V(c) = V(R) p.d across the cell - not EMF, as doesn’t take into account V(r)

Question 18

Working out EMF and internal resistance

Answer 18

• rearrange EMF = I(R + r) to
EMF = V(c) + Ir (expanding, V=IR)
• rearrange that to V(c) = -Ir + EMF
• find values, plot graph of V(c) on y axis, I on x axis.
• gradient is -internal resistance; EMF is y intercept

Question 19

Potential divider equation

Answer 19

• V(1) = R(1)/R(1)+R(2) x V(c)

* for resistors in series - unravel parallel resistors first!