Resistance and I- V Characteristics

Question 1

For some components, as current through them is changed. The resistance of the component changes as well.

Answer 1

1) The resistance of ohmic conductors change with current. At a constant temperature, the current flowing through an ohmic conductor id directly proportional to the PD across it.
2) The resistance of some resistors and components does change e.g. diode or filament lamp

Question 2

How does resistance increase for filament lamp ?

Answer 2

When electrical charges flow through a filament lamp, it transfers some energy to the Thermal energy store of the filament , which is designed to heat up. Resistance increases with temp, so as current increases, the filament lamp heats up more and resistance increase.

Question 3

How does resistance work for filament lamp ?

Answer 3

For diodes, the resistance depends on the direction of current , they will happily let current flow in one direction but have a very high resistance if it is reversed.

Question 4

what is I-V characteristics ?

Answer 4

graphs which shows the current (I) flowing through a component changes as the PD ( v) ACROSS IT IS INCREASED.

linear components have an I - V characteristic that’s a straight line.

non- linear components have an curved I - V characteristic

Question 5

I-V characteristics PRACTICAL 1-3

Answer 5

1) Set up the test circuit ( check page (181)
2) begin to vary the variable resistor. This alters the current flowing through the circuit and the PD across the component

3) Take several pairs of readings from the Ammeter and voltmeter to see how the PD across the component varies as the current changes. Repeat each reading 2 more to get an average pd at each current

Question 6

I-V characteristics PRACTICAL 4-6

Answer 6

4) Swap over the wires connected to the cell, so the direction of the current is reversed

5) plot a graph of current against voltage for the component

Question 7

IV characteristics for ohmic conductor page 181

Answer 7

STRAIGHT

the current through an ohmic conductor is directly proportional to pd so you get a straight line

Question 8

IV characteristics for filament lamp
page 181

Answer 8

As current increases, the temp of filament increases. This means less current can flow per unit pd, so the graph gets shallower - hence the curve

Question 9

IV characteristics for diode
page 181

Answer 9

current will only flow through a diode in 1 direction. The diode has very high resistance in reverse direction.