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Physics (old) > chapter 8 & 9 > Flashcards

chapter 8 & 9 Flashcards

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1
Q

define current

A

the rate of flow of charged particles
I = Q/t

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2
Q

how is current measured?

A

ammeter in series,
lowest resistance as possible to not affect readings

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3
Q

what is 1 ampere?

A

1 ccoulumb of charge flowing throw a point at 1 second

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4
Q

what is a charge carrier?

A

any partcle with an electrical charge
* electrons
* ions

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5
Q

what is current in
* metals
* electrolytes?

A
  • electrolytes: movement of ions
  • metals - movement of delocalised electrons
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6
Q

what is the elementary charge?

e

A

the charge of an electron
-1.6 * 10 ^-19

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7
Q

describe charge

A

A property of matter : quanitised by electrons

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8
Q

what is kirchoff’s law?

A

Σ I in= Σ I out

conservation of charge

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9
Q

what is the ‘number density’?

A

the number of free charge carriers per unit of volume

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10
Q

how does the number denisty impact a material?

A

the greater the number density, the better the electrical conductor

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11
Q

what are the 3 groups of materials?

A
  • conductors (10^28)
  • semi conductors (10^17)
  • insulators
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12
Q

what is the formula for current?

A

I= Anev
* A= area of cross section
* n= number density
* e= elementary charge
* v= mean drift velocity

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13
Q

derive the Anev equation

A
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14
Q

what is drift velocity?

A

the average velocity of the charges moving along a conductor

not uniform journey as collides with positive metal ions

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15
Q

what is the realtionship between the cros sectional area and the mean drift velocity?

A

inversley proprtional
* as the area increases the number of positive metal ion and distrubance for electrons increases and so the mean drift veloity would be smaller

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16
Q

what is the direction of conventional current

A

positive- negitive : used for all diagrams

electron flow : negative - positive

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17
Q

explain the term mean drift velocity of electrons in a metal wire

A
  • free electrons make collisions with metal ions to give them a random velocity
  • the free electrons drift towards the positive end the supply along the wire
  • the distance travelled per unit time along the length of wire is called the mean drift velocity of the electrons
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18
Q

draw the symbols for the following:
* cell
* battery
* lamp
* resistor
* variable resistor
* thermistor
* LDR
* diode
* LED (light emitting diode)
* ammeter
* voltmeter

A
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19
Q

what is the nragtive and positive side of the terminal?

A

positive: long
negative: short

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20
Q

what is potnetial difference defined as?

A

the change in potential energy per unit chrage between two points, due to charge doing work on the circuit components, causing electrical potential energy to decrease

work done per charge carrier

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21
Q

what is the equation for potential difference?

A

V = W/Q
* V= potential difference
* W= difference between electrical energy
* Q= per unit charge

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22
Q

what is the difference of 1 volt?

A

the potential difference between two points when a charge of 1 coulumb passing through the two points experiences a change in electric potential energy (1J)

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23
Q

what do voltmeters measure?

A

the difference in electric potenteial energy per harge

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24
Q

how are voltmeters positioned, why do they have high resistance?

A

in paralle
* they have high resistance to make sure that the component is not short circuited

25
Q

how do you calculate the kinetic energy of an electron?

A
26
Q

define the electro motive force

A
  • measures the work done to charge carriers when they gain energy at the power supply
  • energy transfered from chemical–> electrical
    ε = W/Q where ε = electromotive force (in Volts), W = work done (in Joules) and Q = charge (in Coulombs)

the output

27
Q

what is the kinetic energy of electrons?

A

when a potential difference accelerates a charged particle, the energy transfered is equal to the kinetic energy gained by the particle (usually an electron)

28
Q

what is resistance?

A
  • opposition to current (electrons flowing through)
  • resistance=p.d across component/current in component
29
Q

what is 1 ohm?

A

the resistance of a components that has a p.d of 1v flowing per 1 amph of current

30
Q

what is ohms law?

A

which temperature of a (ohmic) comductor is constant, the current is directly proportional to the p.d

r is constant

31
Q

what happens as temperature increases to resistance?

A
  • kinetic energy increases
  • metal ions vibrate at a higher amplitude
  • oppose the motion of electrons creating resistance
32
Q

draw IV graph for resistor

A
33
Q

draw an IV graph for a filament light bulb

A
34
Q

draw an IV graph for a diode/LED

A
35
Q

what determines whether the current has a negative or posititve reading?

A

the positioning of the battery

36
Q

how does the resistance change as the current is increased?

A
  • current increases means more electrons collide with metal ions
  • ions then vibrate with a greater amplitude (temo ibraeses)
  • more work done on charge carriers (electrons)
  • harder for electrons to flow through circuit
  • current increases
37
Q

what happens at a diode when the p.d is above the threshold voltage?

A

the resistance is very small and current is large

38
Q

what is the LDR?

A

light depedant resistor
* as light intensity increases
* light fslls releasing electrons (free charge carriers)
* resistance decreases

39
Q

What is the total resistance?

A
  • the number of free charge cariers per unit volume (number density) is low
  • resistance is high
40
Q

what is an ohmic conductor?

A

one where the current is directly propertion to the p.d

40
Q

An ohmic conductor has a resistance of 12 Ohms when a voltage of 3V is applied across it. What would the resistance be if 9v was applied across it?

A

12 ohms because it is an ohmic conductor and the temperature stays constant

41
Q

what happen to charge carriers in term of energy at the power supply and at the components?

A
  • at the power supply: charge carriers gain energy
  • components: charge carriers loose energy
42
Q

what is a negative temperature coefficent (NTC) thermistor ?

A
  • as the temperature increases the reistance decreases
  • the number density of free charge carriers increases with temperature
43
Q

draw the IV graph for a thermistor

A
44
Q

What is the equation for resistivity and the units?

A
45
Q

Why is the cross sectional area and the resistance of a wire inversely proportional?

A

Analogy: the amount of water passing is a lot more with a wide pipe than with a really narrow pipe.
With a larger cross sectional area, more charge carriers can pass through

46
Q

what is resitivity?

A
  • the property of a material
  • independant of shape and size (unlke resistance)
  • a constant that only chnages if temperature changes
  • higher resitivity = higher resistance
47
Q

how does resitivity change in metals with increasing temperature?

A
  • metals: as temp increeases, fixed metal ions vibrate at a greater frequnecy and amplitude= increased collisions, incresaed resistance and resistivity
  • semi conductors: as temp increases (n) free numer density increases an so resistance decrease sand resistivity
48
Q

Describe the practical on how to measure the resistivity of a wire

A
49
Q

What is a resistivity of 1 ohm meter ?

A

1 ohm meter is when a cubic meter of material has a resistance of 1 ohm

50
Q

A wire has a resistivity of 0.005 Ωm. What would the resistivity be if the length of the wire was doubled and the diameter was halved? Give your answer in Ωm.

A

0.005 Ωm becuase resistivity is not affected by length/diameter

51
Q

What are the equations for power (4)?

A
52
Q

What does this equation fundamentally mean?

P=IV

A

As the current or p.d increases then the more power is being transferred

53
Q

What is the equation for the energy transferred in electrical circuits?

A
54
Q

What is the kilowatt hour?

A

A unit of energy equal to 1kW of power usage for 1 hour

A.k.a the “unit”

55
Q

How many joules are in 1 kilowatt hour

A
56
Q
A
57
Q

what is the difference between the emf and p.d?

A
  • emf: charges gain energy
  • pd: charges loose energy
  • emf: chemical energy turns electrical
  • pd: electrical energy to heat/ other forms
  • emf and p.d work done by charges (Volts)

Physics (old) (10 decks)

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