Resistance

Question 1

Resistance

Answer 1

Ratio of the potential difference across it to the current flowing through it
R=V/I
Unit: ohm

Question 2

Measuring resistance

Answer 2

Ammeter + voltmeter using the formula
Ohmmeter will measure the resistance directly

Question 3

Ohm’s Law

Answer 3

At a constant temperature the current flowing through the conductor is directly proportional to the p.d. through them
If material obeys ohm’s law they are said to be Ohmic conductors

Question 4

Variable resistor - rheostat

Answer 4

Moving the sliding contact we can change the amount of wire that the current has to flow through , more it flows through the greater the resistance

Question 5

Factors effecting resistance of conductors

Answer 5

Temperature
Length
Cross-sectional area
Material its made of

Question 6

Temp on metals/ conductors

Answer 6

Temp increases, the atoms vibrate more causing more collisions with the electrons moving. Hence its resistance increases
As electrons move they collide with the atoms which resist their motion more collisions greater the resistance

Question 7

Temp on insulators and semiconductors

Answer 7

Increasing the temp decreases the resistance
In insulators and semiconductors most of the electrons are not free to move in the material as they are attached to a particular atom
Temp increase causes more electrons to gain enough energy to break loose from the atoms and flow as electric current
This overcomes the increase in vibration and collisions of electrons

Question 8

Thermistor (thermal resistor)

Answer 8

Semiconductor whose resistance decreases rapidly with increasing temperature

Question 9

Resistivity

Answer 9

Resistance = resistivity x length / cross-sectional area
Unit: Ohmmetre