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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

How does conventional current flow?

A

Positive to negative

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2
Q

Current in a series circuit

A

Current is the same everywhere in the circuit

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3
Q

What is current?

A

The rate of flow of electrons around a circuit

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4
Q

Current and charge equation

A

Q=IT

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5
Q

Voltage and charge equation

A

V=W/Q

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6
Q

Kirchhoff’s 2nd law

A

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

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7
Q

EMF

A

Energy transferred by the battery per unit charge

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8
Q

Resistance in series

A

Rtotal=R1+R2+R3….

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9
Q

Ideal circuit

A

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

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10
Q

Voltage in parallel circuits

A

The same across the branches

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11
Q

Kirchoff’s 1st law

A

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

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12
Q

Resistance in parallel circuits

A

1/Rtotal=1/R1 + 1/R2 + 1/R3 …

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13
Q

Ohmic conductor

A

A component that obeys Ohms law

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14
Q

Ohms law

A

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

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15
Q

What is the gradient of an IV graph

A

1/R

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16
Q

How to check if a component obeys ohms law

A

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

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17
Q

Variable resistors

A

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

Slider changes length of wire so current can flow through

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18
Q

Experiment to test if something is an ohmic conductor

A

-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

19
Q

Examples of non ohmic components

A

-Bulb
-Thermistor
-LDR
-Diode

20
Q

Explain the shape of filament bulb IV graph

A

-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

21
Q

Why do filament bulbs blow?

A

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

22
Q

Examples of semi conductors

A

Thermistor
LDR

23
Q

Insulators

A

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

24
Q

Semi conductors

A

Somewhere inbetween conductors and insulators

25
Q

How do semiconductors work

A

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

26
Q

Diodes

A

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

27
Q

Disadvantage of series circuit

A

If one element breaks none of the others will work

28
Q

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

A

-The current will be higher
-Because resistance opposes current

29
Q

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

A

-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

30
Q

Practical use of diodes

A

Protects against current surges

31
Q

Power equations

A

P=E/t
P=VI
P= I²R
P=V²/R

32
Q

EMF equations

A

ℰ=I(R+r)
ℰ=V+Ir

33
Q

Internal resistance for cells in series

A

Internal resistance adds together

34
Q

Internal resistance for cells in parallel

A

Internal resistances don’t add together

35
Q

Why does terminal voltage fall as current increases?

A

When the variable resistor has a high resistance it makes the current smaller.

It uses a larger share of the EMF

36
Q

Potential divider equation

A

Vout= R2/(R1+R2) x Vin

37
Q

Variable resistor vs potentiometer

A

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

38
Q

.

A

.

39
Q

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

A

-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

40
Q

What causes internal resistance inside a battery?

A

The electrons collide with atoms inside the battery

41
Q

Superconductor

A

A component with no resistance below or at critical temperature

42
Q

Uses of superconductors + reason

A

-Electromagnets
-Generators

-Very high magnetic field strength
-Less energy loss

43
Q

Define potential divider

A

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

44
Q

Explain why resistance increases as voltage increases

A

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

Physics (10 decks)

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