Electricity Flashcards
Define Current, its units and base units
the rate of flow of charge per unit time, amperes, [Cs-1 ]
What is the equation linking I, Q and t
-
I = Q/t
- [Cs-1]= C/s
What is the elementary charge, e ?
1.6 x 10-19C
What must the charge on any object be?
It must be an integer of the elementary charge, expressed as Q = ne ; where n is the number of electrons either added or removed
modelling electric current in metals
how can the structure of a metal be thought of as
a regular crystal structure or lattice of positive ions, surrounded by a number of delocalised electrons.
why may there be a larger current in a circuit?
- a greater number of electrons moving past a given point each second
- the same number of electrons moving faster through the metal
what is conventional current
it is when current flows from a positive terminal towards a negative one, it is opposite the flow of electrons
what is an electrolyte, and what are its charge carriers
it is a liquid, ionic solution, that can carry an electric current , the electric current is a flow of ions
what happens if salt is dossolved in water
as it is an ionic solution the salt seperates into positivley charged sodiumions, cations , Na+ , and negativey charged chlorine ions, anions, Cl-. If an anode and cathode are placed in the solution, ions are attracted to the electrode. when the Na ions reach the cathode they accept an electron and the Cl ions donate an electron
what is used to measure current
Ammeters are used to measure the electrical current at any point in a circuit, placed in series
what is an important property of ammeters
they should have the lowest possible resistance in order to reduce the effect they have on the current. the ideal ammetrer has 0 resistance.
What does the conservation of charge state
electric charge can neither be created nor destroyed, the total amount of electric charge in the universe is constant.
What is kirchhoff;s first law
- the sum of currents into a junction is equal to the sum of current leaving a junction
- ∑Iin = ∑Iout
what is number density
it is the number of free charge carriers per unit volume
what is the average number density of conductors, semi conductors and insulators
- 1029 m-3
- 1019 m-3
- 109 m-3
What is an equation for I, linking, I,A,n,e,v
I = A n e v
what is the effect of changing the cross sectional are of a wire
the narrower the wire the greater the drift velocity must be in order for the current to be the same
Why does increasing the temperature increase resistance
as temp increases the positive ions have more internal energy and vibrate with greater amplitude about their mean positions. the frequency of collisions between the charge carriers and the positive ions increases, so the charge carriers too more work to transfer more energy as they travel
what is potential difference
it is a measure of the transfer of energy by charge carrier
what is one volt equal to
- 1 V = 1 J C-1
*
What is the equation for Voltage
V = W/Q
What is used to measure voltage and how
a voltmeter is used in parallel, it should have infinite resistance so that no current passes through the voltmeter itself
potential difference Is used to describe…
when work is done by the charge carriers, they are losing energy as they pass through the component.