Electricty

Question 1

What is Ohm’s Law?

Answer 1

For a metal conductor current is directly proportional to voltage so long as temperature is constant

Question 2

Define current

Answer 2

Flow of charge

Question 3

Define potential difference

Answer 3

Energy transferred from electrical to other forms per unit charge

Question 4

Define emf

Answer 4

Energy available to be converted to electrical energy per unit charge

Question 5

Define resistance

Answer 5

A property of a component that regulates electric current

=potential difference
—————————
current

Question 6

Define mean drift velocity

Answer 6

Average displacement travelled of the electrons along the wire per second

Question 7

Kirchhoff’s 1st Law:

Answer 7

The sum of the current entering a junction is equal to the sum of the current leaving a junction (charge is conserved)

Question 8

Define resistivity

Answer 8

A measure of how strongly a material opposes the flow of electric current, ratio of the product of resistance and cross sectional area and its length

Question 9

Define power

Answer 9

Rate of work done or energy transfer

Question 10

Kirchhoff’s 2nd Law:

Answer 10

The algebraic sum of the emfs and the pds is equal to 0 (conservation of energy)

Question 11

Define terminal pd

Answer 11

Energy transferred from electrical energy to other forms per unit charge

=emf-lost volts

Question 12

Define internal resistance

Answer 12

The resistance that cause the lost volts

Question 13

Define the electron volt

Answer 13

Energy an electron gains when its accelerated across a pd of 1 volt

Question 14

Define an amp

Answer 14

1A is the same as 1 coulomb of charge passing a point in 1 second

Question 15

Which way is conventional current?

Answer 15

From + to -

Question 16

Which way is electron flow?

Answer 16

From - to +

Question 17

Define a coulomb

Answer 17

1C is the charge that flows past a point in 1 sec when there is a current of 1A

Question 18

Equation including drift velocity

Answer 18

I=nAve

Where 
I=current
n=amount of charge carriers per cubic metre
A=cross sectional area
v=drift velocity
e=charge value

Question 19

What’s the difference between pd and emf

Answer 19

Both are energy transfer per unit charge it emf is from chemical to electrical and pd is from electrical to other forms

Question 20

Define the volt

Answer 20

1 volt is the potential difference between 2 points when 1 joule of work is done to move 1 coulomb

Question 21

Define an ohm

Answer 21

1 ohm is the resistance of a component that has a pd of 1 volt per ampere of current

Question 22

Current=

Answer 22

Q
—
t

Question 23

What causes a substance to either be a conductor, semi-conductor or insulator?

Answer 23

For conductors the electrons are very free to move around and so the value of n for the substance is high. For semi conductors the electrons are locked down until energy is put in to it, examples of these are thermistors and LDRs. For insulator n is very small and so there aren’t many free electrons at all to carry the charge to create a current

Question 24

Equation for the energy transfer of charged particles

Answer 24

eV=0.5mv^2

Question 25

Resistance=

Answer 25

Potential Difference
—————————
Current

Question 26

As light intensity increases, the resistance of an LDR….

Answer 26

Decreases

Question 27

As temperature increases the resistance of a thermistor….

Answer 27

Decreases

Question 28

Power=

Answer 28

Potential difference x current

OR

current x current x resistance

OR

p.d x p.d
—————-
resistance

Question 29

Define the kilowatt-hour

Answer 29

Energy transferred by a device working 1kW for 1 hour

Question 30

Sum for the total resistance of resistors in series

Answer 30

R=R1+R2

Question 31

Sum for the total resistance of resistors in series

Answer 31

1 1 1
— = — + —
R R1 R2

Question 32

Equation including internal resistance

Answer 32

E=I(R+r)

E=V+Ir

E=emf
V=potential difference
I= current
R=resistance in circuit
r=internal resistance

Question 33

What are circuits called when the pd is shared between the components?

Answer 33

Potential dividers

Question 34

V(out)=

Answer 34

R1
——— x V(in)
R1+R2