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Physics AS > Chapter 9 > Flashcards

Chapter 9 Flashcards

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1
Q

What is a battery?

A

2 or more cells connected in series

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2
Q

What is the resistance of ammeters and voltmeters?

A

Ammeter have a resistance of 0 or near zero

Voltmeters have a resistance on infinity

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3
Q

Define potential difference

A

Work done by charge carriers per unit of charge

Measures the energy transferred by charge carriers as they pass through component which make them transfer the energy

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4
Q

Define 1 volt

A

The PD across a component when 1 J of energy is transferred per unit charge passing through a component

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5
Q

What is the formula of PD

A

V = W/Q

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6
Q

Define electromotive force

A

The work done to charge carriers per coulomb as they pass through a cell or battery

Energy transferred to electrical energy from chemical per unit charge

AKA voltage in

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7
Q

What is the formula for electromotive force?

A

E = W/Q

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8
Q

What does an electron gun do?

A

Produces and accelerates a narrow beam of electrons which have precise kinetic energies

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9
Q

How does an electron gun work?

A

Metal filament is heated by electric current(cathode)
Electrons gain kinetic energy and some have enough to leave the surface of the metal (THERMIONIC EMISSION)
The circuit is in a vacuum tube with a high PD between cathode and anode so electrons accelerate(and gain energy)
The anode has a hole in it so electrons can pass as a beam with a specific kinetic energy

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10
Q

What is the formula for velocity of electrons?

A

eV = 1/2 mv^2

Charge of electron x PD = 1/2 mass x velocity^2

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11
Q

What does a higher PD mean?

A

The electrons have more energy so the beam moves faster

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12
Q

Define resistance

A

The PD across a component divided by the current passing through the compound

A component has a resistance of 1ohm if a potential difference of 1V makes a 1A current flow

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13
Q

What does higher resistance mean?

A

Higher resistance means that it takes higher energy to push charge carriers

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14
Q

How can resistance be determined experimentally?

A

Set up a circuit with a variable power supply, ammeter in series and voltmeter in parallel
Draw a graph of IV
The reciprocal of the gradient is the resistance

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15
Q

What is Ohms law?

A

For a metallic conductor at a constant temperature, current is directly proportional to PD across the ends

Components are ohmic if they follow this law

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16
Q

What is the effect of temperature on resistance?

A

As a wire gets hotter:
Positive ions vibrate with greater amplitude about a fixed position
Frequency of collisions with charge carriers and ions increase
Charge carriers have to do more work to pass
This increases resistance so more energy must be transferred for charge carriers to travel

17
Q

What does a shallow gradient of an IV graph show?

A

Greater resistance

18
Q

What do the IV graphs of resistors and filament lamps look like?

A

Straight line and wavy line

19
Q

What are diodes?

A

Components made from semiconductors which allow current to flow in only one direction

They have forward bias and infinite resistance in the opposite direction

20
Q

What are LED’s?

A

Diodes which emir a single wavelength if light when they conduct

21
Q

What is the graph characteristics of a diode?

A

It is a non ohmic conductor as PD is not directly proportional to I

22
Q

Explain resistance in a diode

A

Has a threshold voltage of 0.69 v where resistance drops. This happens because number density of charge carriers increase

Before 0.69v the resistance is infinite

23
Q

What is a thermistor? What do they do and how do they work?

A

A component made from a semiconductor which has a negative temperature coefficient.
Resistance decreases as temperature increases because increasing temperature causes bonds to break which releases electrons so number density increases

24
Q

What does ntc mean?

A

Negative temperature coefficient: resistance drops as temperature increases because of bonds breaking which increase number density

25
Q

What is the characteristic graph of a thermistor?

What is the graph of resistance vs temperature

A

Same as filament lamp
Non ohmic
PTC is wavy the other way
Goes from top left to bottom right as a curve and asymptote

26
Q

What is a LDR?

A

A light dependent resistor where resistance changes depending on light intensity
It is made from semi conductors
As light intensity increases, number density increases so resistance decreases

Non ohmic relationship(same as resistance temp graph for thermistor)

27
Q

What factors affect resistance?

A

Material of wire and it’s resistivity
Length of wire
Cross sectional area

28
Q

Define resistivity

A

The physical property of a material. It is the resistance of a 1m length of wire with a 1m2 cross sectional area

Unit: ohm meters

Same for any shape at a given temperature

29
Q

What are the relationships between resistance, length, area

A

R is directly proportional to length(longer wire means larger pd)
R is inversely proportional to the area

30
Q

What is the formula for resistivity?

A

Resistivity(ohm meters) = RA/L

Resistivity at a given temperature is the product of resistance and cross sectional area divided by length

31
Q

What is resistivity from a graph?

A

Gradient of a resistance length graph multiplied by area

32
Q

Define power

A

The rate of energy transfer or work done per unit time

P=W/t

33
Q

What are the formulae one must know for power?

A

P=W/t
P=I^r
P=V^2/R
P=IV

34
Q

How do you do you find total energy?

A

Just multiply by time

W=IVt
W=I^2 R t
W=v^2/R t

35
Q

What is a kilowatt hour?

A

Energy transferred by a device with a power of 1 kW operating for an hour

36
Q

How do you calculate energy in KwH

A

E(kWH)=P(kW)xt(Hours)

Physics AS (6 decks)

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