Electricity

Question 1

How does conventional current flow?

Answer 1

Positive to negative

Question 2

Current in a series circuit

Answer 2

Current is the same everywhere in the circuit

Question 3

What is current?

Answer 3

The rate of flow of electrons around a circuit

Question 4

Current and charge equation

Answer 4

Q=IT

Question 5

Voltage and charge equation

Answer 5

V=W/Q

Question 6

Kirchhoff’s 2nd law

Answer 6

In a series circuit the sum of the voltages of each component must equal the voltage across the power supply

Question 7

EMF

Answer 7

Energy transferred by the battery per unit charge

Question 8

Resistance in series

Answer 8

Rtotal=R1+R2+R3….

Question 9

Ideal circuit

Answer 9

-Wires have no resistance
-Ammeters are an series and have no resistance
-Voltmeters should be in parallel and have infinite resistance

Question 10

Voltage in parallel circuits

Answer 10

The same across the branches

Question 11

Kirchoff’s 1st law

Answer 11

The current going into a junction must equal the current leaving the junction

Question 12

Resistance in parallel circuits

Answer 12

1/Rtotal=1/R1 + 1/R2 + 1/R3 …

Question 13

Ohmic conductor

Answer 13

A component that obeys Ohms law

Question 14

Ohms law

Answer 14

The voltage across a component is directly proportional to the current flowing through it. Provided physical conditions stay constant

Question 15

What is the gradient of an IV graph

Answer 15

1/R

Question 16

How to check if a component obeys ohms law

Answer 16

-Reverse current direction by reversing connections on battery
-If line on graph remains straight then it’s an ohmic conductor because R is constant

Question 17

Variable resistors

Answer 17

Long coil of wire current flows in one end and out through slider

Slider changes length of wire so current can flow through

Question 18

Experiment to test if something is an ohmic conductor

Answer 18

-Use a variable resistor to change I and V
-Collect 7 sets of data
-Must reverse current flow at some point by flipping battery
-Collect results and plot a graph

Question 19

Examples of non ohmic components

Answer 19

-Bulb
-Thermistor
-LDR
-Diode

Question 20

Explain the shape of filament bulb IV graph

Answer 20

-Initially wire in bulb is cold with low resistance
-Electrons bump into atoms in the wire transferring energy heating up wire
-Lattice of atoms vibrate more so it’s harder for electrons to come through
-So R increases

Question 21

Why do filament bulbs blow?

Answer 21

-Wire starts cold so R is low
-This allows very high current
-This heats wire up rapidly
-Quick change in temperature can break wire

Question 22

Examples of semi conductors

Answer 22

Thermistor
LDR

Question 23

Insulators

Answer 23

Very few charge carriers (electrons) available so current can’t flow easily

Question 24

Semi conductors

Answer 24

Somewhere inbetween conductors and insulators

Question 25

How do semiconductors work

Answer 25

If you supply energy to a semiconductor in the form of heat/light you can release extra charge carriers So R will change depending on Light/Tenperature

Question 26

Diodes

Answer 26

-Only lets current flow in one direction -When voltage is higher than threshold (0.6 to 0.7 V)

Question 27

Disadvantage of series circuit

Answer 27

If one element breaks none of the others will work

Question 28

Why is it an advantage for a rechargeable battery to have a low internal resistance?

Answer 28

-The current will be higher -Because resistance opposes current

Question 29

Why is a filament lamp likely to fail when it’s switched on?

Answer 29

-It’s initially cold with a low resistance -This allows for a large current at the start -This causes a rapid change in temperature which can break the lamp

Question 30

Practical use of diodes

Answer 30

Protects against current surges

Question 31

Power equations

Answer 31

P=E/t P=VI P= I²R P=V²/R

Question 32

EMF equations

Answer 32

ℰ=I(R+r) ℰ=V+Ir

Question 33

Internal resistance for cells in series

Answer 33

Internal resistance adds together

Question 34

Internal resistance for cells in parallel

Answer 34

Internal resistances don’t add together

Question 35

Why does terminal voltage fall as current increases?

Answer 35

When the variable resistor has a high resistance it makes the current smaller. It uses a larger share of the EMF

Question 36

Potential divider equation

Answer 36

Vout= R2/(R1+R2) x Vin

Question 37

Variable resistor vs potentiometer

Answer 37

Variable resistor: -Can vary current but not as sensitively -Cannot get 0 -Easier to connect Potentiometer -Can vary sensitively -From 0V to EMF -Harder to connect

Question 38

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Answer 38

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Question 39

Why does the resistance of an NTC thermistor decrease when temperature increases?

Answer 39

-As it heats up more charge carriers become available (electrons) -The increased internal energy liberates electrons -More charge can be carried through meaning the resistance has decreased -More electrons is more significant than the additional vibration of lattice ions

Question 40

What causes internal resistance inside a battery?

Answer 40

The electrons collide with atoms inside the battery

Question 41

Superconductor

Answer 41

A component with no resistance below or at critical temperature

Question 42

Uses of superconductors + reason

Answer 42

-Electromagnets -Generators -Very high magnetic field strength -Less energy loss

Question 43

Define potential divider

Answer 43

A set of 2 or more resistors connected across a voltage source used to split EMF

Question 44

Explain why resistance increases as voltage increases

Answer 44

As voltage increases, more electrons move through the wire More collisions between these electrons and ions in the lattice Vibration of lattice ions increases So number of collisions per second increases Increasing resistance