Electricity experiments Flashcards
(54 cards)
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
2
Q
verify Joule’s Law - graph
A
x-axis: I² (A²)
y-axis: rise in temp (C)
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
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
5
Q
verify Joule’s Law - how graph verifies Joule’s law
A
graph is a straight line through origin verifying
ΔΘ ∝ I²
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)
7
Q
Joule’s law formula
A
P = I²R
8
Q
verify Joule’s Law - sources of error
A
- ensure same time period used each time
- ensure fresh cold water used each time
9
Q
verify Joule’s Law - reducing heat loss
A
- polish the calorimeter
- use lid
- use short time period as possible
- insulation (styrofoam)
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
11
Q
Measure resistivity of a material of wire - describe how data was collected
A
resistance: ohmmeter
length: metre stick
diameter: vernier callipers
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
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
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
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
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
17
Q
Measure resistivity of a material of wire - effect of doing experiment on a warmer day
A
-resistance increased
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
19
Q
variation of resistance with temp - metallic conductor - graph
A
x-axis: temp (C)
y-axis: R (ohms)
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
21
Q
variation of resistance with temp - a thermistor - graph
A
x-axis: temp (C)
y-axis: R (ohms)
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
variation of resistance with temp - metallic conductor - use graph to estimate change of resistance with respect to temp
slope from graph
26
variation of resistance with temp - metallic conductor - use graph to estimate resistance resistance when it is immersed in melting ice
-use intercept
27
variation of resistance with temp - thermistor - how resistance was measured
- 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
variation of resistance with temp - thermistor - how temp was varied
-using a bunsen burner
29
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)
- 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
variation of resistance with temp - thermistor -why immersed in oil rather than water
- 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
variation of resistance with temp - metallic conductor - estimate resistance at temp of -20 using graph
- get slope and equation of line using slope formula and line formula (y = mx + c)
- use line equation to find R
32
variation of resistance with temp - metallic conductor - estimate change in resistance for a temp increase of 80 degrees (2008 qs)
-find difference in resistance between points where temp is 0 and 80 on graph
33
variation of resistance with temp - metallic conductor - use graph to explain why relationship between resistance of metallic conductor and its temp is linear
-a straight line is obtained
34
variation of resistance with temp - metallic conductor - use graph to explain why relationship between resistance of metallic conductor and its temp is NOT linear
- linera only for a narrow range of temperature
| - R is non-linear at high T
35
variation of resistance with temp - sources of error
-wait until temp has stopped rising before taking a reading, otherwise leads to inaccurate results
36
Variation of current (I) with potential difference (V) - metallic conductor - method
- 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
Variation of current (I) with potential difference (V) - filament bulb - method
- 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
Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - method
- 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
Variation of current (I) with potential difference (V) - semiconductor diode - method
- 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
Variation of current (I) with potential difference (V) - why does resistance of a filament change with its pd?
- as pd increases, current increases
- as current increases temp increases
- as temp increases resistance increases
41
Variation of current (I) with potential difference (V) - bulb - use resistance vs temp experiment to explain shape of graph
- temp increases as current increases
| - resistance increases as temp increases
42
Variation of current (I) with potential difference (V) - metallic conductor - device used to vary pd + device used to measure he pd
- vary using variable resistor (rheostat)
| - measure pd from voltmeter across diode
43
Variation of current (I) with potential difference (V) - metallic conductor - how rheostat varied the pd
-moved sliding contact
44
Variation of current (I) with potential difference (V) - metallic conductor - explain shape of graph
-resistance of conductor increases with increasing temp
45
Variation of current (I) with potential difference (V) - metallic conductor - resistance of diode
- resistance not constant
| - not proportional to V, as graph is not a straight line through the origin
46
Variation of current (I) with potential difference (V) - metallic conductor - what adjustments should be made when connections to the semiconductor diode are reversed?
- microammeter used instead of milliammeter
| - voltmeter placed across diode + microammeter
47
Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - how pd was changed
-adjusting rheostat
48
Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - use graph to calculate resistance of the electrolyte
- 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
Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - observation at electrodes as current flowed through electrolyte
- cathode coated with fresh copper / cathode got heavier
| - anode got lighter
50
Variation of current (I) with potential difference (V) - semiconductor diode - what is the junction voltage
i dont fucking know bc i cant find an explanation anywhere, but i think its where the line starts to exponentially rise
51
Variation of current (I) with potential difference (V) - filament bulb - why current not proportional to pd, explain using graph
not a straight line graph
52
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)
find R at 1V, then R at 5V and subtract to find change
53
Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - how to help copper to stick to electrodes
use a drop of sulphuric acid
54
Variation of current (I) with potential difference (V) - copper sulphate with copper electrodes - why use a drop of sulphuric acid
help copper stick to electrodes
