Mod 4: charge and current Flashcards
What equation shows the net charge on a particle
Q= +- ne. Where n is the number of electrons added or removed
What is the structure of a metal
A lattice of positive ions surrounded by delocalised electrons
How does solid metal conduct electricity
(Structure) one side of the metal is made to be positive and the other is made to be negative so the electrons will be attracted to the positive so current will flow through the structure
How does NaCl solution conduct electricity
The electrolyte NaCl contains +ve and -ve ions therefore the electrolyte will split into Na+ cations and Cl- anions so when a pair of electrodes are place in the solution the cations will be attracted to the cathode and the anions will be attracted to the anode. This produces an electrical current
Which is the +ve and _ve electrode
Anode= positive
Cathode= negative
What is conventional current
The flow of positive charge that moves in the opposite direction of electrons (+ve- -ve)
Describe the electron flow in a metal
It is in the opposite direction of conventional current
What is Kirchohoff’s first law
For any point in an electrical circuit the sum of the currents in to that point is equal to the sum of currents out of that point. This law is a consequence of conservation of charge as charge can not be created or destroyed.
What is mean drift velocity
The average rate of change of displacement of the charge carriers in a substance
Why does mean drift velocity happen
When e- move through a metal they frequently collide with the positive metal ions resulting in the random movement.
What does the number density n represent
The number of charge carriers per unit m^3
Describe the number density n in conductors vs insulators
- the value n is much higher in conductors than in insulators therefore the e- in insulators must travel faster in order to carry the same current than the n in conductors
What does the V stand for in the equation
I=neV/dt
V=volume
What is the volume of a wire equal
The cross sectional area of the wire A x by its length
What is the time taken for the e- to cross the wire equal to
The mean drift velocity
How do we find the number n using an equation
N = Q/ e. ( E = elementary charge)
What is the net charge on a particle a multiple of
It is the multiple of e (elementary charge)
How was the conventional current defined as
A flow of positive charge
What is n the number density
The number of charge carriers per m^3
What is drift velocity
The average rate of change of displacement of the charge carriers in a substance
How do electrons travel
-ve to +ve
A vertical transmitter aerial emits an em wave to a reactive that has a diode in its circuit. Explain why this is necessary for the receiver aerial to receive info
The current induced by the aerial is alternating so the diode rectifies this so info can be transmitted
Which electrical quantity has the s.i unit of amperes per second
Charge
What is elementary charge
The smallest unit that charge come in.
What is the specific word to describe charge as a multiple of e
Quantised
How many volts does 1JC^-1 equal to
1 V
What is the energy transferred to a charged particle that is accelerated by a p.d equal to
The work done on the particle
: W=VQ.
W=Ve
What is the unit for n in I=AneV
Metre^-3
What is the n in perfect insulators and real insulators
0
Real insulators have very few n
Is ionic crystals a conductor or an insulator
Insulator however once molten the liquid will conduct
Describe an electrolyte
A substance that contains ions and conducts electricity when molten
How may a gas become a conductor
When u apply a high enough voltage electrons will get ripped out of atoms making a spark, and giving u ions along a path
What is the shape of the graph of the power of a fixed resistor that changes with current and why
Power is directly proportional to current squared therefore the graph will be a quadratic
The lowest value at which an led lights up is 0.5V explain why this means ther is minimum energy transferred to the led
Because the minimum amount of p.d was supplied for current to flow through the diode and transfer energy
Explain why the power dissipated by an LED in the forward direction is much less than the reverse direction
The resistance of the diode in the reverse direction is much greater and
P= V^2 / R
Therefore power is much lower in that direction as power is inversely proportional to resistance
What is the is base unit for energy
Kgm^2s^-2
Why does the light intensity increase in an LDR when the resistance decreases
Because the number density of charge carriers increases
What quantity is conserved in Kirchhoff law 1st
Charge
Define a coulomb
The charge which passes a point when a current of 1 amp flows for one second
State the difference between the direction of conventional current and the charge flow in a metal wire
Charge flow in a metal is in the opposite direction of conventional current however in a metal electrons flow
Describe mean drift velocity and the motion of electrons in a wire
The distance travelled along the wire each second, the electrons move in randomly but they all still drift towards the positive terminal
