Flashcards in Electricity Deck (137)
What is current?
It is the rate of flow of charge
Explain the water pipe analogy for current
The amount of water that flows depends on the flow rate and the time
What equation links charge, current and time?
Q = IT
What is the charge carried by in an electrical circuit?
Charge is carried through the wires by electrons
What is the unit of charge?
What is 1 coulomb defined as?
The amount of charge that passes in 1 second when the current is 1A
Do you attach an ammeter in series or in parallel in an electrical circuit?
Why do you attach an ammeter in series?
So the current through the ammeter is the same as the current through the component
Which way does conventional current flow (in terms of + and -)?
+ve to -ve
Which way do electrons flow (in terms of + and -)?
-ve to +ve
Why do electrons flow from -ve to +ve?
Because electrons are negative, they are repelled by the negative and attracted to the positive
When a charge flows through a component, what does it do?
It transfers energy to the component
What do you need to do to make electrical charge flow through a circuit?
You need to transfer energy to the charge
Where does the energy needed to transfer energy to the charge come from?
A power source e.g. a battery
In a DC circuit, compare the speeds of the electrical current and the electrical energy
The electricity within the wires flows very slowly; at speeds around inches per minute. At the same time, the electrical energy flows at nearly the speed of light
What happens to the charge when it flows through the power source?
It is 'raised' through the potential (meaning it's voltage is raised) and energy is transferred to the charge as electrical energy
Explain how the power source does work?
It does work to move the charge around the circuit by transferring energy
What is potential difference?
The work done in moving a unit of charge between 2 points
What equation links potential difference, work done and charge?
V = W/Q
What is 1 volt equal to?
1 joule per coulomb
Explain, using the water analogy, potential difference
The p.d. is like the pressure that's forcing water along the pipe
Do you attach a voltmeter in series or parallel?
Why do you attach a voltmeter in parallel?
Because it has a high internal resistance
Why do voltmeters have an almost infinite resistance?
So only a tiny current can flow through it because it only needs a small amount of current to measure the p.d.
What is resistance?
A measure of how difficult it is for current to flow
What is the p.d. and current if a component has a resistance of 1Ω?
A p.d. of 1V making a current of 1A flow through it
What equation links resistance, potential difference and current?
R = V/I
Who did most of the early work on resistance?
Georg Simon Ohm
What is Ohm's Law?
A rule to predict how the current would change as the potential difference is increased for certain types of conductor