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LC Physics > Electricity experiments > Flashcards

Electricity experiments Flashcards

1
Q

verify Joule’s Law - method

A
  • fill cal to immerse coil
  • pour water into grad cylinder + record volume, pour back into cal
  • set up as per diagram
  • turn on current, adjust variable resistor so current of -/5A flows
  • turn off current
  • place thermom into water + record lowest, steady reading + start clock
  • record reading on ammeter
  • allow current to flow for set no. of mins, stirring throughout
  • keep current steady by adjusting variable resistor
  • when time is up, turn off current
  • record highest temp
  • pour out water + refill with same vol of cold water
  • repeat steps for diff values of I, the current. Keep time interval + current supplied constant for each run
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2
Q

verify Joule’s Law - graph

A

x-axis: I² (A²)

y-axis: rise in temp (C)

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3
Q

verify Joule’s Law - using graph to find a temp when a certain current is used

A
  • square the i first, as the graph is in i², then find it on graph and use to find temp
  • the temp is the rise in temp, so add that temp to initial temp to find the temp we’re looking for
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4
Q

verify Joule’s Law - why fixed mass of water used

A
  • power req for temp rise is proportional to mass

- otherwise there would be too many variables

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5
Q

verify Joule’s Law - how graph verifies Joule’s law

A

graph is a straight line through origin verifying

ΔΘ ∝ I²

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6
Q

verify Joule’s Law - how to use graph to find resistance of heating coil (2006 qs)

A

RI²t = mcΔΘ

this is derived from P=W/t
P is = to RI² (Joule’s Law)

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7
Q

Joule’s law formula

A

P = I²R

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8
Q

verify Joule’s Law - sources of error

A
  • ensure same time period used each time

- ensure fresh cold water used each time

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9
Q

verify Joule’s Law - reducing heat loss

A
  • polish the calorimeter
  • use lid
  • use short time period as possible
  • insulation (styrofoam)
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10
Q

Measure resistivity of a material of wire - method

A
  • straighten wire as much as possible
  • select points where ohmmeter probes go
  • connect probes together + reset to zero to negate resistance in wires
  • attach probes to wire at designated points
  • measure distance between points using metre stick, this is the length l
  • measure + record resistance displayed on ohmmeter
  • zero the vernier callipers + wire placed between its jaws. Tighten over wire. Repeat 3 times at diff points along wire + get average value for diameter
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11
Q

Measure resistivity of a material of wire - describe how data was collected

A

resistance: ohmmeter
length: metre stick
diameter: vernier callipers

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12
Q

joule’s law - calculate slope of graph and hence the resistance of the heating coil

A 
slope = y2-y1/x1-x1
slope = Rt/mc
RI²t = mcΔΘ 
Slope = ΔΘ/I²
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13
Q

Joule’s law - slope

A

Slope of the line will be more or less equal to the values of ΔΘ/I² obtained in table

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14
Q

Measure resistivity of a material of wire - how to ensure wire was of uniform diameter

A
  • measure diameter at diff points + get average diameter

- no kinks

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15
Q

Measure resistivity of a material of wire - proceedure in measuring length of wire

A
  • straighten

- measure distance between points for which resistance was measured

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16
Q

Measure resistivity of a material of wire - steps in finding average diameter of wire

A
  • zero the digital callipers
  • place wire between jaws
  • tighten jaws + take reading
  • repeat for diff points on wire
  • get average diameter
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17
Q

Measure resistivity of a material of wire - effect of doing experiment on a warmer day

A

-resistance increased

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18
Q

variation of resistance with temp - metallic conductor - method

A
  • connect ohmmeter probes together, reading displayed is internal resistance of probes
  • connect coil to ohmmeter to get resistance of coil
  • fill beaker w/ cold water + set up as per diagram
  • leave equip to adjust to temp of water.
  • Record temp + resistance displayed when there is a steady reading on thermometer
  • apply heat source, allow temp of glycerol to rise by 5, remove heat source. When steady reading - record temp + resistance
  • repeat until at 100°C
  • subtract internal resistance of probes from resistance readings
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19
Q

variation of resistance with temp - metallic conductor - graph

A

x-axis: temp (C)

y-axis: R (ohms)

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20
Q

variation of resistance with temp - a thermistor - method

A
  • connect ohmmeter probes together, reading displayed is internal resistance of probes
  • connect thermistor to ohmmeter to get resistance of thermistor
  • fill beaker w/ cold water + set up as per diagram
  • leave equip to adjust to temp of water.
  • Record temp + resistance displayed when there is a steady reading on thermometer
  • apply heat source, allow temp of glycerol to rise by 5, remove heat source. When steady reading - record temp + resistance
  • repeat until at 100°C
  • subtract internal resistance of probes from resistance readings
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21
Q

variation of resistance with temp - a thermistor - graph

A

x-axis: temp (C)

y-axis: R (ohms)

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22
Q

Measure resistivity of a material of wire - sources of error

A
  • Ensure temp of room remains constant. Solids, liq, gases expand when heated. Temp of room may cause wire to expand, diameter + length of wire will increase, causing resistance to increase.
  • Wire must be free of bends + kinks + remain taut to ensure correct measurement for length taken. Percentage error occurs when using a metre stick
  • length taken between two probe contact points, not incl the actual points of contact
23
Q

variation of resistance with temp - wire - describe relationship from graph

A
  • straight line
  • linear/proportional relationship
  • R increases with T
24
Q

resistance vs temp graphs

A

learn how to graph for diff materials

25
Q

variation of resistance with temp - metallic conductor - use graph to estimate change of resistance with respect to temp

A

slope from graph

26
Q

variation of resistance with temp - metallic conductor - use graph to estimate resistance resistance when it is immersed in melting ice

A

-use intercept

27
Q

variation of resistance with temp - thermistor - how resistance was measured

A
  • connect ohmmeter probes together, reading displayed is internal resistance of probes
  • connect thermistor to ohmmeter to get resistance of thermistor
  • apply heat source
  • resistance displayed on ohmmeter recorded when there is a steady reading on thermometer for each temp
  • subtract internal resistance of probes from readings to get resistance of thermistor for each temp
28
Q

variation of resistance with temp - thermistor - how temp was varied

A

-using a bunsen burner

29
Q

variation of resistance with temp - thermistor -use graph to estimate average variation of resistance per kelvin in the range 45°C-55°C (2010 qs)

A
  • get the difference in resistance between these two temps on the graph, and then divide by 10 as there is a 10 degree temp difference
  • unit: Ω K⁻¹ (for this question)
30
Q

variation of resistance with temp - thermistor -why immersed in oil rather than water

A
  • oil is a better conductor of heat
  • it heats gradually so its easier to regulate than water
  • water contains air
  • impure water conducts electricity
31
Q

variation of resistance with temp - metallic conductor - estimate resistance at temp of -20 using graph

A
  • get slope and equation of line using slope formula and line formula (y = mx + c)
  • use line equation to find R
32
Q

variation of resistance with temp - metallic conductor - estimate change in resistance for a temp increase of 80 degrees (2008 qs)

A

-find difference in resistance between points where temp is 0 and 80 on graph

33
Q

variation of resistance with temp - metallic conductor - use graph to explain why relationship between resistance of metallic conductor and its temp is linear

A

-a straight line is obtained

34
Q

variation of resistance with temp - metallic conductor - use graph to explain why relationship between resistance of metallic conductor and its temp is NOT linear

A
  • linera only for a narrow range of temperature

- R is non-linear at high T

35
Q

variation of resistance with temp - sources of error

A

-wait until temp has stopped rising before taking a reading, otherwise leads to inaccurate results

36
Q

Variation of current (I) with potential difference (V) - metallic conductor - method

A
  • adjust rheostat until pd across coil is 1V
  • measure + Record pd V across current I through coil
  • increase pd (adjust rheostat)
  • record pd + current again
  • repeat until there are a no. of readings
37
Q

Variation of current (I) with potential difference (V) - filament bulb - method

A
  • adjust rheostat until pd across bulb is 1V
  • measure + Record pd V across current I thru bulb
  • increase pd (adjust rheostat)
  • record pd + current again
  • repeat until there are a no. of readings
38
Q

Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - method

A
  • adjust rheostat until pd across electrolyte is 1V
  • measure + Record pd V across current I thru electrolyte
  • increase pd (adjust rheostat)
  • record pd + current again
  • repeat until there are a no. of readings
39
Q

Variation of current (I) with potential difference (V) - semiconductor diode - method

A
  • ensure diode in forward bias
  • adj rheostat until pd is at smallest possible value
  • record pd V across current I thru diode
  • adjust rheostat, inc the pd by 0.2V
  • record pd + current again
  • repeat until current is less than 50 mA
  • reverse connections on diode. Make adjustments..
  • repeat steps taken for when in forward bias
40
Q

Variation of current (I) with potential difference (V) - why does resistance of a filament change with its pd?

A
  • as pd increases, current increases
  • as current increases temp increases
  • as temp increases resistance increases
41
Q

Variation of current (I) with potential difference (V) - bulb - use resistance vs temp experiment to explain shape of graph

A
  • temp increases as current increases

- resistance increases as temp increases

42
Q

Variation of current (I) with potential difference (V) - metallic conductor - device used to vary pd + device used to measure he pd

A
  • vary using variable resistor (rheostat)

- measure pd from voltmeter across diode

43
Q

Variation of current (I) with potential difference (V) - metallic conductor - how rheostat varied the pd

A

-moved sliding contact

44
Q

Variation of current (I) with potential difference (V) - metallic conductor - explain shape of graph

A

-resistance of conductor increases with increasing temp

45
Q

Variation of current (I) with potential difference (V) - metallic conductor - resistance of diode

A
  • resistance not constant

- not proportional to V, as graph is not a straight line through the origin

46
Q

Variation of current (I) with potential difference (V) - metallic conductor - what adjustments should be made when connections to the semiconductor diode are reversed?

A
  • microammeter used instead of milliammeter

- voltmeter placed across diode + microammeter

47
Q

Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - how pd was changed

A

-adjusting rheostat

48
Q

Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - use graph to calculate resistance of the electrolyte

A
  • get slope, which will be the inverse of the resistance as resistance if V/I not I/V
  • flip it and it will be the actual resistance
  • take an R value and A value from graph and use R = V/I
  • Make sure to convert mA to A before calculations
49
Q

Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - observation at electrodes as current flowed through electrolyte

A
  • cathode coated with fresh copper / cathode got heavier

- anode got lighter

50
Q

Variation of current (I) with potential difference (V) - semiconductor diode - what is the junction voltage

A

i dont fucking know bc i cant find an explanation anywhere, but i think its where the line starts to exponentially rise

51
Q

Variation of current (I) with potential difference (V) - filament bulb - why current not proportional to pd, explain using graph

A

not a straight line graph

52
Q

Variation of current (I) with potential difference (V) - filament bulb - calculate change in resistance of filament bulb as pd increases from 1V to 5V (2005 qs)

A

find R at 1V, then R at 5V and subtract to find change

53
Q

Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - how to help copper to stick to electrodes

A

use a drop of sulphuric acid

54
Q

Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - why use a drop of sulphuric acid

A

help copper stick to electrodes

LC Physics (25 decks)

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