CGP AS Section 6 - Electricity Flashcards
What is current?
Current is the rate of flow of charge
Define a coulomb:
One coulomb (C) is defined as the amount of charge that passes in 1 second if the current is 1 ampere (A)
How can you measure current?
Using an ammeter
-needs to be connected in series
What is voltage?
Potential difference or voltage, is defined as the work done (energy converted) per unit charge moved.
How do you measure voltage?
Using a voltmeter
-needs to be connected in parallel to the component
Define a volt:
The potential difference across a component is 1 volt when you convert 1 joule of energy moving 1 coulomb of charge through the component
What is resistance?
A components resistance is a measure of how difficult it is o get current to flow through it (measured in ohms)
What does resistance in a circuit mean to the energy transfer going on?
-when electricity flows through them, they heat up and some of the electrical energy is wasted as thermal energy
How can you lower the resistivity of a material?
by cooling a material down
What if you cool some materials down below a critical transition temperature?
their resistivity disappears entirely and they become a superconductor
What can a material being a superconductor mean to the energy transfers that occur?
-without any resistance, none of the electrical energy is turned into heat, so none wasted
What would happen if you started a current flowing in a superconductor circuit?
if you started a current flowing with a magnetic field and then take away the magnet the current would carry on flowing forever
What are the challenges of using superconductors?
-the critical temperatures are really low (below 10 kelvins) and getting things that cold is hard and really expensive
What do solid state physicists do to do with superconductors?
they are trying to develop room-temperature superconductors (managed to get a metal oxide things to superconduct at about 140K)
What are the uses of superconductor wires?
- power cables that transmit energy without loss of power
- strong electromagnets that don’t need a constant power source (for medical use and for Maglev trains)
- electronic circuits that work really fast, as there’s no resistance to slow them down
Define power:
is the rate of transfer of energy (measured in watts (W) where 1 watt = 1 joule per second)
Where does resistance in a circuit come from?
from electrons colliding with atoms and losing energy to other forms
How does a battery work in a circuit?
chemical energy is used to make electrons move
-as the electrons move they collide with atoms inside of the battery so batteries must have resistance (this is called internal resistance)
What makes batteries and cells warm up in a circuit?
internal resistance
What is e.m.f.?
Electromotive force (not an actual force,measured in volts) -it's the amount of electrical energy the battery produces for each coulomb of charge
What is the terminal p.d.?
-the potential difference across the load resistance (R) is the energy transferred when one coulomb of charge flows through the load resistance
What would be true in a circuit if there was no internal resistance?
-the terminal p.d. would be the same as the e.m.f.
(in real power supplies there is always some energy lost overcoming internal resistance
What are lost volts?
the energy wasted per coulomb overcoming the internal resistance
What does the conservation of energy tell us about internal and external resistance?
energy per coulomb supplied by the source = energy per coulomb transferred in the load resistance + energy per coulomb in internal resistance
