3.1 - Electrical Quantities

Question 1

What is current and what way does conventional current flow

Answer 1

rate of flow of charge (of negatively charged particles)
flows from + to -

Question 2

what way does the actual charge flow in a circuit

Answer 2

• to +

Question 3

what is the formula for current

Answer 3

I = Q/t

Question 4

what is resistance and the formula

Answer 4

Opposition to the flow of current
Resistance = voltage / current
Ohms = V / I

Question 5

what is ohms law and the conditions

Answer 5

• states voltage is proportional to current
• resistance will remain constant
• temperature is constant

Question 6

what is the relationship between current and p.d in fixed resistors (graph shape)

Answer 6

• when potential difference across a fixed resistor changes, the current changes by the same percentage
• straight line

Question 7

what is the relationship between current and p.d in a diode

Answer 7

• has a low resistance if the p.d is in one direction, but very high if p.d is in the opposite direction (forward biased)
• does not obey ohms law as resistance changes

Question 8

what is the relationship between current and p.d in a filament lamp (shape)

Answer 8

• when p.d increases across the filament lamp bulb, current also increases. Increased current increases resistance
• s - shaped graph
• obeys ohms law at low values

Question 9

what is a variable thermistor

Answer 9

a resistor whose value can be changed

Question 10

what happens to resistance of a thermistor at high and low temperatures

Answer 10

• at low temperatures resistance is high
• at high temperature resistance is low
• negative temperature coefficient: as temperature increases, resistance decreases

Question 11

how does resistance very on an LDR

Answer 11

• as light intensity increases, resistances decreases

Question 12

what is voltage and the formula

Answer 12

• a measure of the amount of energy a component transfers per unit of charge passing through it
• voltage = energy transferred / charge passing

Question 13

what is emf

Answer 13

electromotive force - amount of energy supplied to each unit of charge

Question 14

what is potential difference

Answer 14

when a component in an electrical circuit is using and transferring energy to other forms

Question 15

what is the electron volt and how to you convert between joules and eV

Answer 15

• amount of energy an electron gains by passing through a potential difference of 1v
• 1 eV = 1.6x10^-19J

Question 16

what is the resistivity of a material

Answer 16

the same value as the resistance between opposite faces of a cubic metre of the material

Question 17

what is the relationship between resistance with length of a wire, cross sectional area

Answer 17

Resistance is proportional to length of wire, but inversely proportional to cross sectional area

Question 18

what does n, e, v and A represent in the transport equation

Answer 18

n - number of charge carriers per unit volume
e - charge of the carriers
v - drift velocity
A - cross sectional area of wire