Electricity (E)

Question 1

Current:

Answer 1

The rate of flow of positive charge carriers

Question 2

What is current measured in?

Answer 2

Amps

Question 3

equation relating time, charge and current

Answer 3

charge = current x time (Q=It)

Question 4

What is conventional flow:

Answer 4

flow of charge from positive to negative

Question 5

What is electron flow?

Answer 5

Negatively charged electrons flow from negative terminal of cell to positive.

Question 6

What measures current?

Answer 6

An ammeter in series

Question 7

What is potential difference?

Answer 7

the work done per unit charge in volts

Question 8

Equation relating potential difference and work done:

Answer 8

potential difference = work done/charge

Question 9

Resistance:

Answer 9

the opposition to current

Question 10

The higher the resistance…

Answer 10

the lower the current

Question 11

Why are wires often made of copper?

Answer 11

As they have very low resistance so are very good electrical conductors

Question 12

equation for resistance, potential difference and current

Answer 12

resistance = potential difference / current

Question 13

what is an ohm?

Answer 13

one volt per amp

Question 14

State Ohm’s law:

Answer 14

For a conductor at a constant temperature, the current through it is proportional to the potential difference across it.

Question 15

How can you investigate Ohm’s law?

Answer 15

adjusting a variable resistor to vary the current in the circuit. Measure voltage across fixed resistor as current varies. Draw graph.

Question 16

How can you tell form a graph if a component obeys Ohm’s law?

Answer 16

straight line through the origin

Question 17

Draw diode current voltage graph:

Answer 17

straight line on x axes until a little after origin on x axes it goes steeply upwards

Question 18

Draw filament lamp current voltage graph:

Answer 18

initially follows ohmic component trend but as voltage gets too high, current flattens

Question 19

Resistivity describes:

Answer 19

The extent to which a material opposes the flow of electric current through it

Question 20

What happens as free electrons move through metal wire?

Answer 20

they collide with ions, transferring their energy upon collision

Question 21

what is resistivity measured in?

Answer 21

ohm metres

Question 22

higher resistivity=

Answer 22

higher resistance

Question 23

What does higher temp do to resistance and why?

Answer 23

Higher temp means ions inside wire vibrate faster so there are more collisions, slowing them down so current decreases

Question 24

What does a thermistor do?

Answer 24

As the temperature increases, the resistance decreases.

Question 25

Draw symbol for thermistor:

Answer 25

---box with hockey stick through it-----

Question 26

What is superconductivity?

Answer 26

If a material is below a temperature called the critical temperature, its resistivity disappears entirely. it is now a superconductor

Question 27

What are superconductors useful for?

Answer 27

applications that require a large electric field or reductions of energy loss

Question 28

name 4 uses of superconductors:

Answer 28

MRI scanners, transformers, motors, electromagnets

Question 29

What does a light dependant resistor do?

Answer 29

As the light intensity increases the resistance decreases.

Question 30

Resistors in series:

Answer 30

combined resistance of components = sum of all individual resistances (Rt = R1 + R2 + R3...)

Question 31

Resistors in parallel:

Answer 31

reciprocal of combined resistance = reciprocal of individual resistances (1/R = 1/R1+ 1/R2 ...)

Question 32

Current in series:

Answer 32

current is same for all components

Question 33

Current in parallel:

Answer 33

current is split across branches. total current in junction = total current out of a junction

Question 34

Potential difference in series:

Answer 34

emd is shared amongst all components depending on their resistance

Question 35

Potential difference in parallel:

Answer 35

voltage of all components in each branch = emf

Question 36

Charge is never...

Answer 36

used up or lost

Question 37

What is KIRCHHOFF's first law?

Answer 37

sum of currents entering a junction = sum of currents coming out of a junction (I = I1 + I2 +....)

Question 38

junction:

Answer 38

point where at least three circuit paths meet

Question 39

branch:

Answer 39

point connecting two junctions

Question 40

Energy is never...

Answer 40

used up or lost

Question 41

What is KIRCHHOFF's second law?

Answer 41

the total emf in a closed circuit equals the sum of the potential difference across each component (each closed circuit can be treated like a series circuit)

Question 42

The sum of emfs in each closed loop =

Answer 42

emf of power supply

Question 43

What is electrical power?

Answer 43

rate of change of work done

Question 44

Power equation (wd and time) :

Answer 44

work done / time

Question 45

What is work done?

Answer 45

Energy transferred

Question 46

Power equation (current and voltage)=

Answer 46

current x voltage

Question 47

Using Ohm's law, how can you rewrite the power equation?

Answer 47

P=I^2R or P=V^2/R

Question 48

How can you calculate energy transferred?

Answer 48

voltage x current x time

Question 49

When two resistors are connected in series...

Answer 49

through K's second law, the p.d across the power source divides between the two

Question 50

Potential dividers:

Answer 50

circuits which produce an output voltage as a fraction of its input voltage

Question 51

What are the three main purposes of potential dividers?

Answer 51

to provide variable potential differences, to enable specific pd to be chosen, to split pd of a power source between two or more componenets

Question 52

V out =

Answer 52

(R2/R1+R2) x V in