Module 4 Practicals Flashcards
1
Q
Investigating the electrical characteristics for a range of ohmic and non-ohmic components
- Method (4)
- Graphs and Calculations (1)
- Safety (1)
- Validity (5)
A
- Set up a circuit that includes a power supply, a variable resistor, an ammeter and the component of interest all in series, as well as a voltmeter across the component
- Vary the voltage across the component by changing the resistance of the variable resistor
- For each voltage, record the current 3 times and calculate the mean
- Repeat this for different components
- Plot a graph of mean current against voltage for each component
- Be careful as the components may heat up
- Switch off the circuit in between readings to prevent heating of components
- Use a wide range of voltages
- Control the equipment used and the temperature of the area
- To reduce uncertainty take more readings at more voltages
- To reduce uncertainty use ammeters and voltmeters with greater resolution
2
Q
Determine the resistivity of a wire
- Method (4)
- Graphs and Calculations (2)
- Safety (2)
- Validity (1)
A
- Measure the diameter of the wire using a micrometer
- Measure at 3 different points and calculate a mean
- Attach the wire to a circuit with a power supply, an ammeter and a voltmeter across the wire
- Adjust the length of the wire, measuring the current and voltage each time
- Repeat the experiment twice more and calculate a mean resistance for each length
- Calculate the cross sectional area of the wire
- Plot a graph of resistance against length
- Gradient = p/A (R=pL/A)
- Wear safety goggles in case wire snaps
- Disconnect crocodile clips between measurements to avoid them heating up
- Switch circuit off in between reading to avoid heating components
3
Q
Determining the internal resistance
- Method (3)
- Graphs and Calculations (1)
- Validity (1)
A
- Set up a circuit which includes a power supply, a variable resistor, an ammeter, a switch and a voltmeter across the power supply
- Set variable resistor to max value and measure current and voltage across power supply
- Adjust variable resistor and repeat
- Plot graph of V against I
- V= -rI + E
- Open the switch between readings to prevent heating of the variable resistor
4
Q
Determining the maximum power of a cell
- Method (3)
- Graphs and Calculations (3)
- Safety (1)
- Validity (1)
A
- Set up a circuit which includes a power supply, a variable resistor, an ammeter, a switch and a voltmeter across the power supply
- Set variable resistor to max value and measure current and voltage across power supply
- Adjust variable resistor and repeat
- Calculate the power supplied by the battery for each reading using P=IV
- Calculate the resistance for each reading using R=V/I
- Plot a graph of power against resistance
- It should have an arched shape in which the peak of the arch shows the maximum power of the cell
- This peak occurs when the variable’s resistor is equal to the internal resistance of the cell
- Don’t use a high voltage as components could become too hot
- Use a range of resistances on the variable resistor to see the trend in the graph more easily
5
Q
Investigating circuits with more than one source of emf
- Method (4)
- Graphs and Calculations (2)
- Safety (3)
- Validity (1)
A
- Set up the first circuit containing two cells in series, a resistor and a voltmeter over the resistor
- Record the reading on the voltmeter
- As the resistor is the only component this will be the potential difference supplied by the cells
- Set up the second circuit the same as the first, except place the two cells in parallel and repeat
- Repeat the entire experiment with cells of different voltages
- Calculate the expected combined potential difference for each combination
- Series: emf = sum of emfs
- Parallel: emf = the same across each branch
- Compare the theoretical combined potential difference and the actual p.d.
- Do not connect 2 cells of different voltages in parallel as this could lead to overheating and sparks
- Do not use high voltage cells to minimise risk of electrocution
- The resistor may get hot so be careful when touching it
- There will be some error in the value for the overall emf due to internal resistance
6
Q
Using non-ohmic devices as sensors
- Method for LDR (4)
- Method for Thermistor (6)
- Graphs and Calculations (1)
- Safety (2)
- Validity (1)
A
- Set up a circuit containing a power supply, an LDR, and a fixed resistor all in series as well as a voltmeter across the fixed resistor
- Record the voltage across the resistor for the initial light intensity
- Increase the light intensity and record the new values for light intensity and voltage
- Repeat until light intensity cannot be increased any further
- Set up a circuit containing a power supply, a waterproof thermistor, and a fixed resistor all in series as well as a voltmeter across the fixed resistor
- Place the thermistor into boiling water
- Measure the temperature of the water using a thermometer
- Record the voltage across the resistor for the initial temperature
- Place some ice in the water
- Record the voltages and temperatures for every 5 degrees decrease in temperature
- Plot a graph of voltage against light intensity/temperature
- Careful not to trip when room is dark
- Be careful when handling boiling water
- Make sure the surrounding area is as dark as possible
7
Q
Using an oscilloscope to determine the frequency and amplitude of a wave
- Method (3)
- Graphs and Calculations (1)
- Validity (3)
A
- Connect a microphone to an oscilloscope and play a note into the microphone
- Read off the time base the oscilloscope is set to (the scale of the x axis)
- Find the amplitude of the wave by reading off the distance from the middle line to the highest point on the wave
- Determine the frequency of the wave using f = 1/T where T = distance between peaks x time base setting
- Each horizontal division on the screen represents a unit of time
- The time base control varies the seconds/milliseconds per division
- You can reduce the uncertainty in the frequency measurement by altering the time base such that one full wave has the widest possible range in the x direction
8
Q
Observing polarising effects using microwaves and light
- Method for Light (3)
- Method for Microwaves (3)
- Safety (2)
- Validity (1)
A
- Hold a polarising filter up to eye level
- Place another filter behind it and rotate it
- Observe that when the filters are perpendicular, no light gets through
- Place a vertically aligned metal grille in front of the transmitter (which transmits vertically plane polarised waves)
- Place a detector behind the grille
- Place another grille behind the first grille and rotate it, observing whether the detector records any microwaves as the position of the grille changes
- Do not look directly into a bright light
- Microwaves can cause burns if their intensity is too high so don’t stand in front of the transmitter when it is on
- Make sure the detector is working and the waves are vertically aligned by turning on the transmitter and checking the detector receives the waves with and without the detector
9
Q
Investigating refraction and total internal reflection of light
- Method for Semi Circular Block (4)
- Method for Rectangular Block (6)
- Graphs and Calculations (1)
- Safety (1)
- Validity (2)
A
- Place the block on a piece of paper and draw around it
- Make a mark at the centre of the straight edge and draw a normal from the point
- Shine a ray of light from a ray box towards the curved edge of the block in an arc until the ray emerges along the surface of the boundary between the material and air
- Measure the angle the ray makes with the normal using a protractor - this is the critical angle
- Place the block on a piece of paper and draw in pencil around it
- Lift the block and draw a normal line on the piece of paper
- Place the block back on the page and aim the beam at the point where the normal line meets the block
- Trace the beal line entering and exiting the block
- Measure the angle of incidence (angle between the incident ray and the normal) and the angle of refraction (angle between refracted ray and the normal)
- Repeat this rotating the beam by 10 degrees each time
- Calculate the refractive indexes of both blocks
- Semi circular use: n = 1/sin C
- Rectangular use: n = sin i/sin r
- Don’t shine the light at anyone or at reflective surfaces
- Ensure the beam is directed towards the same point each time
- Use a thinner laser for more accurate results
10
Q
Investigating refraction and reflection in a ripple tank
- Method (3)
A
- Use a motorised straight edged bar to produce plane waves while a small dipper produced circular waves
- Shine a light from above so that the wave pattern can be seen below the tank
- From the shadow, measure the wavelength of the water waves and investigate the angles of reflection and refraction
11
Q
Investigating superposition using microwaves
- Method (5)
- Graphs and Calculations (2)
- Safety (1)
- Validity (2)
A
- Remove the turntable wheels from the microwave so that the plate is stationary
- Place the chocolate on the turntable and place it back in the microwave
- Turn on the microwaves for 30 seconds
- Take the chocolate out and observe the pattern of melted and solid strips
- Using a ruler, measure the distance between 4 melted strips
- Divide the distance between the strips by 3 to find the distance between adjacent melted strips
- Multiply this distance by 2 to find the wavelength of the microwaves
- Microwaves can cause burns
- Use a longer bar of chocolate to reduce the uncertainty in the measurements
- Use a bar of chocolate with uniform thickness to make it easier to see where the antinodes are as the thinner parts will melt faster in a non uniform bar
12
Q
Determining the wavelength of light using a diffraction grating
- Method (3)
- Graphs and Calculations (2)
- Validity (3)
A
- Shine the laser through the diffraction grating onto the screen
- Measure the distance between the central fringe and the one beside it
- Measure the distance between the grating and the screen
- Calculate 𝜃 using tan 𝜃 = distance between fringes/distance between grating and screen
- Use: dsin 𝜃 = nλ to calculate the wavelength (d will say on the grating itself and n = 1)
- Calculate the wavelength using the 2nd and 3rd orders and find an average (the percentage uncertainty in 𝜃 is decreased if 𝜃 is as large as possible)
- Conduct in a dark room so the different fringes can be seen
- Use a monochromatic light source
13
Q
Determine the wavelength of a colour of light using diffraction from a CD
- Method (4)
- Graphs and Calculations (1)
A
- Measure the radius of the CD, r
- Place the CD in front of a lamp that is behind you and move the CD away from your eye until the chosen colour light is on the edge of the CD
- Measure the distance from the disk to your eye, D
- Repeat for other colour of light
- Calculate the angle of diffraction using tan 𝜃 = r/D
14
Q
Determine the speed of sound in air by the formation of stationary waves in a resonance tube
- Method (4)
- Graphs and Calculations (2)
- Safety (1)
- Validity (1)
A
- Fill the resonance tube halfway with water
- Hit a tuning fork with a hammer and hold it above the tube
- Lower an open ended measuring cylinder into the water until the intensity of the sound is amplified, this is when resonance is heard
- Measure the current height of the cylinder out of the water
- Calculate the wavelength of the sound by multiplying the current height by 4
- Find the speed of sound by multiplying the wavelength by the frequency of the tuning fork
- Don’t let the tuning fork touch the resonance tube as the vibrations can break the tube
- Repeat the experiment 3 times and calculate a mean wavelength
15
Q
Determine the Planck constant using LEDs
- Method (5)
- Graphs and Calculations (1)
- Validity (1)
A
- Set up a circuit to include a power supply and a fixed resistor in series with a diode connected to a potential divider connected to the fixed resistor
- Also include an ammeter and a voltmeter in the potential divider part of the circuit
- Find the wavelength of the LED from its packaging
- Find the threshold voltage of the LED by recording the potential difference at which the LED starts to emit light
- Repeat with different LEDs
- Plot a graph of voltage against 1/wavelength
- eV = hc/λ → Vλ = hc/e
- Make sure LED is in a dark box in a dark room
