AS1 1.10 Resistance and Resistivity

Question 1

Current and Voltage in Series Circuits

Answer 1

In a series circuit, current stays the same but voltage splits up

Question 2

Current and Voltage in Parallel Circuits

Answer 2

In a parallel circuit, current splits but voltage stays the same.

Question 3

Resistance in Parallel Equations

Answer 3

I(total) = I(1) + I(2)
I(total) = V / R(total)
V / R(total) = V / (R1) + V / (R2)
1 / R(total) = 1 / (R1) + 1(R2)….

Question 4

What is resistivity?

Answer 4

Resistivity is the resistance of 1m of material 1m^2

Question 5

Resistivity Equation

Answer 5

R = pL / A p = RA / L
R = Resistance (ohms)
L = Length (metres)
A = Area ( m^2)
p = Resistivity

Question 6

What is critical (or transition) temperature?

Answer 6

Critical (or transition) temperature is the temperature at which a material loses its electrical resistivity and becomes a superconductor

Question 7

What is a superconductor?

Answer 7

A superconductor is a material which loses all its electrical resistivity to become a perfect conductor when it is below its critical (or transition) temperature

Question 8

Applications/Uses of superconductors

Answer 8

1. Production of powerful electromagnets (with no generation of heat)
   -MRI scanners, extremely strong magnetic fields produced
   -Maglev (magnetic levitation), extremely strong magnetic fields produced
2. Transmission of electrical power, power losses greatly reduced due to zero resistance

Question 9

What is Ohm’s Law?

Answer 9

Ohm’s Law is that the potential difference across a conductor is directly proportional to current through it, provided temperature remains constant.

Question 10

What is a diode?

Answer 10

A diode is an electrical device that allows current to move through in one direction with far greater ease than in the other direction.

Question 11

Applications/Uses of diodes

Answer 11

• Protecting components
• Rectifying a voltage
• Controlling signal sizes

Question 12

What is an ntc Thermistor?

Answer 12

A thermistor is a temperature sensing element made of semiconductor material that has been sintered in order to display large changes in resistance in proportion to small changes in temperature

Sintered - the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction
.

Question 13

Applications/Uses of ntc Thermistors

Answer 13

• Temperature measurement (thermostats)
• Temperature compensation
• Temperature control

Question 14

Why does the resistance of an ntc thermistor decrease in relation to temperature?

Answer 14

• As current increases, so does temperature.
• Metal ions vibrate much more, causing electrons to collide with them more often
  -The ntc thermistor is made from semiconducting material, which gives the atoms more energy, more electrons detached for conduction.
• increased number of electrons > vibrations of atoms, hence resistance decreases.

Question 15

explain the IV graph for a filament lamp

Answer 15

• As the P.D is increased , current increases
• temperature increases and metal ions vibrate much more
• electrons collide with metal ions more often
• resistance of circuit increases
• rate of increase of current decreases.

Question 16

Describe the resistance in a VI graph

Answer 16

Low resistance - small gradient
High resistance - large gradient

Question 17

Absolute Zero

Answer 17

The average KE of particles is zero

Question 18

Kelvin to Celcius

Answer 18

-273

Question 19

Celsius to Kelvin

Answer 19

+273