9.7 , 9.8. 9.9 Resistance and resitivity, LDR, Thermistor

Question 1

how does the resistance change as the current is increased?

Answer 1

• current increases means more electrons collide with metal ions
• ions then vibrate with a greater amplitude (temo ibraeses)
• more work done on charge carriers (electrons)
• harder for electrons to flow through circuit
• current increases

Question 2

what happens at a diode when the p.d is above the threshold voltage?

Answer 2

the resistance is very small and current is large

Question 3

what is the LDR?

Answer 3

light depedant resistor
* as light intensity increases
* light fslls releasing electrons (free charge carriers)
* resistance decreases

Question 4

What is the total resistance?

Answer 4

• the number of free charge cariers per unit volume (number density) is low
• resistance is high

Question 5

what is an ohmic conductor?

Answer 5

one where the current is directly propertion to the p.d

Question 6

An ohmic conductor has a resistance of 12 Ohms when a voltage of 3V is applied across it. What would the resistance be if 9v was applied across it?

Answer 6

12 ohms because it is an ohmic conductor and the temperature stays constant

Question 7

what happen to charge carriers in term of energy at the power supply and at the components?

Answer 7

• at the power supply: charge carriers gain energy
• components: charge carriers loose energy

Question 8

what is a negative temperature coefficent (NTC) thermistor ?

Answer 8

• as the temperature increases the reistance decreases
• the number density of free charge carriers increases with temperature

Question 9

draw the IV graph for a thermistor

Answer 9

Question 10

What is the equation for resistivity and the units?

Answer 10

Question 11

what is resitivity?

Answer 11

• the property of a material
• independant of shape and size (unlke resistance)
• a constant that only chnages if temperature changes
• higher resitivity = higher resistance

Question 12

how does resitivity change in metals with increasing temperature?

Answer 12

• metals: as temp increeases, fixed metal ions vibrate at a greater frequnecy and amplitude= increased collisions, incresaed resistance and resistivity
• semi conductors: as temp increases (n) free numer density increases an so resistance decrease sand resistivity

Question 13

Describe the practical on how to measure the resistivity of a wire

Answer 13

Question 14

What is a resistivity of 1 ohm meter ?

Answer 14

1 ohm meter is when a cubic meter of material has a resistance of 1 ohm

Question 15

A wire has a resistivity of 0.005 Ωm. What would the resistivity be if the length of the wire was doubled and the diameter was halved? Give your answer in Ωm.

Answer 15

0.005 Ωm becuase resistivity is not affected by length/diameter

Question 16

Answer 16

Question 17

Answer 17