C8+9

Question 1

Mean drift velocity (2)

Answer 1

• The average displacement/distance travelled of the electrons along the wire in one second
• they move slowly in one direction through the metal (when there is pd across the wire
• they collide constantly / in a short distance with the lattice

Question 2

Kirchhoffs first law (2)

Answer 2

The sum of the currents entering a point is equal to

the sum of the currents leaving that point / junction

Question 3

Ways to describe changes in circuits:

Answer 3

resistance of component decreases
so total circuit resistance decreases
so current increases

Question 4

Ohm’s Law (2)

Answer 4

Current is directly proportional to pd (for a metal conductor)

• provided temperature / all physical conditions remain constant

Question 5

Pd vs emf in terms of energy considerations (2)

Answer 5

Pd: energy transferred per unit charge from electrical form into other forms (e.g. heat / light)

emf: energy transferred per unit charge from other forms into electrical form

Question 6

Define resistance (1)

Answer 6

pd / voltage across a component divided by the current in the component

Question 7

Intensity (1)

Answer 7

energy per unit area per unit time

Question 8

Emf (2)

Answer 8

energy transferred from source / changed from some form to electrical energy

-per unit charge

Question 9

Why is the terminal pd less than the emf (2)

Answer 9

• any source has an internal resistance (1)

- where energy is transferred into thermal energy / lost as that (1)

Question 10

Define kilo-watt hour (1)

Answer 10

(a unit of) energy equal to 3.6 MJ or 1 kW for 1 h/AW