4.2 energy, power and resistance Flashcards
(28 cards)
What is the difference between the symbol for a resistor and a fuse?
both rectangles but fuse had line through it while resistor doesnt
What is the symbol for variable resistor
rectangle with diagonal arrow pointing up and right through it
What is the name of the component whose circuit symbol is a rectangle with two arroes pointing at it
LDR
Voltmeters connected in series or parallel?
parallel
What is potential difference? state units
word done per unit of charge; the difference in potential between two points in a circuit
measured in volts
What does Ɛ represent in electricity?
electromotive force (emf)
What is the difference between voltage and Emf?
voltage is the energy transferred per coulomb across a load resistance
EMF is total amount of work done by battery per coulomb
What is the equation relating energy transferred to voltage
W = VQ
W= work done (energy transferred)
V - pd
Q = charge
T or F: The KE of an electron is multiplied by its charge multiplied by the voltage?
T
energy transferred = eV = 1/2 mv^2
What is resistance?
How difficult it is for current to flow through an appliance
The pd required for each unit of current that flows through a resistor
R = V/I
What is the definition of 1 Ohm?
WHen a resistor is subject to a voltage of 1V and allows a current of 1A through, its resistance is 1 ohm
What is meant by an ohmic conductor?
A conductor that obeys Ohm’s law
What does ohm’s law say?
The current through an ohmic conductor is directly proportional to the potential difference across it. (resistance doesnt vary with voltage or current) - only true if temp is constant
What does the gradient of a current potential diffference graph represent?
1/R
gradient = rise in current/change in potential difference, ie gradient = I/V
resistance = I/V so gradient = 1/R
What would an ohmic conductor graph look like?
a line with a constant gradient that passes through the origin. Shows that voltage is directly proportional to current
For an ohmic conductor, what does a smaller gradient mean?
higher resistance
What does filament lamp graph look like?
S, as current increases, resistance increases
Why does the current increasing on a filament lamp cause an increase in the resistance?
Flow of current causes collisions between the electrons and the metal lattice
These collision increase the temperature of the lattice (and vibration)
As temp increases, more collisions occur, causin resistance to increase
What is a diode?
appliance that only allows current to flow in one direction
What is an LDr
semiconductor that is sensitive to light - as light intensity inc, resistance dec
How does a thermistor work?
similar to LDR, as temp increases resistance decreases - called negative temp coefficient or NTC thermisters
What is resistivity?
shows how easy or difficult it is for current to flow in the material at a specific temp
ρ = RA/L
ρ = resistivity
R = resistance
A = cross sectional area
L = length
Describe an experiment to determine resistivity of a metal
Measure the diameter of your wire using a micrometer
Use this to calc the area
Set up a circuit
Vary length and record the voltage and current for each length
Use R = V/I to work out resistance
Plot a graph of resistance against the length
The gradient = resistivity / area
Rearrange to work out resistivity
T or F: The resistivity of both metals and semiconductors increases with temperature?
F
resistivity of a metal increases with temp veacuase as the metal ions heat up they vibrate more and the electrons bang into them and slow down. Some semiconductors get less resistive as temperature increases, beacuse supplying energy actually causes more charge carriers to be released, so current can flow more easily
