Resistance
Define resistance
Ratio of Voltage/p.d:current.
What direction does a diode allow current to flow
Dorwards
What is the resistivity of a wire with diameter 1.4mm, resistance of 0.5 Ohms, and a length 9.5x as long as two of its circumferences.(2sf)
p=RA/L
[0.5x((1.4x10^-3/2))^2]/9.5x2x1.4x10^-3xpi
2.9x10^-6 Ohm metres
What causes resistance
collisions between electrons and atoms/ions of component or wire
What does a potential divider do
The total resistance of a circuit is 10v. There is only 3 resistors in the circuit. One (in series) has a resistance of 5v. Two more are connected in parallel. One of them has 3x the resistance of the other. What are their resistances?
20/3 Ohms and 20 Ohms
Describe 1 Ohm numerically
1 Volt per Amp
What is an advantage of having a diode in a DC circuit
Protects circuit if voltage is supplied in wrong way (as only allows current in forwards direction)
A wire of current 5A is exposed to 3.5x10^18 positrons per 2 seconds for 10 seconds. What is the new current?
5A = 5C per second
5(1/1.6x10^-19)= 3.125x10^19 electrons per second
ans-(3.5x10^6/18)= 2.95x10^19 electrons per second
2.95x10^19/6.25x10^18 = 4.72A
How do we measure resistance
-Measure current
-Measure p.d
-R=V/I
Draw an I-V graph for a thermistor :
-At high temp
-At low temp
I on y axis, V on x axis.Straight line through origin. Higher temp line has a higher gradient
If the resistivity of a circular wire is equal to its resistance, suggest a suitable measurement of its length and diameter.
Length = area [(d/2)^2 x pie]
Why is total resistance in series = 1/Rt +1/R1 + 1/R2 etc
mention current in series is different blah blah
How much energy is stored in one electron that is part of the following circuit: Resistance of 5 Ohms, Current of 1.6x10^-18 Amps. Consider the electrons rest energy.
=8.0511x10^-18 J