Resistors

Question 1

What are resistors?

Answer 1

Anything which can reduce the flow of current in a circuit

Question 2

Fixed resistor IV graph

Answer 2

Appears as a straight line (current is directly proportional to p.d)

Question 3

Bulb IV graph

Answer 3

Appears S shaped

Question 4

Diode IV graph

Answer 4

Appears as a straight line along the x axis and begins to curve upwards as v gets into positive

Question 5

Ohms law

Answer 5

The current through a component is directly proportional to the p.d across it (provided temperature remains constant)

Question 6

Resistance in LDR’s

Answer 6

Resistance decreases as brightness increases. Used in automatic lights

Question 7

Resistance in thermistors

Answer 7

Resistance decreases as temperature increases. Used in thermostats, fire alarms

Question 8

Core practical - investigate the relationship between p.d, urgent and resistance for a lamp and resistor

Answer 8

1) Connect ammeter in series, bulb in series and variable resistor in series
2) Connect voltmeter in parallel around the bulb
3) Vary the resistance with the variable resistor
4) Record the current (shown on ammeter) and p.d (shown on voltmeter) values
5) Plot an IV graph
6) Repeat with the resistor instead of the lamp

Question 9

Energy transfer in a resistor

Answer 9

Electrical to thermal

-when current flows through a resistor, the electrical energy of the moving charges is transferred to the thermal energy store of the resistor
-when a p.d is applied across the resistor, electrons drift from one end of the resistor to the other, colliding with positive ions and releasing energy
-as energy is transferred to the positive ions they vibrate more and the temperature of the resistor increases

Question 10

Energy transferred equations

Answer 10

Energy transferred (J) = current (A) x p.d (V) x time (s)
Energy transferred (J) = charge (C) x p.d (V)