Physics Experiments on Falling Objects and Resistivity

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Questions and Answers

Describe the method to determine the acceleration of a freely falling object, using an electromagnet.

Open the switch to break the connection between the battery and electromagnet in the primary circuit, and turn on the timer in the secondary circuit.
The electromagnet demagnetizes, causing the steel ball to fall a distance, h, from the bottom of the ball to the top of the trap door. Measure h with a ruler.
When the ball falls through the trap door, it stops the timer.
Record the time taken to fall h. Repeat the process three times, discard anomalies and find the average time.
Vary h and record the corresponding t.

How do you analyse the results from the acceleration of a freely falling object, using an electromagnet?

s = h u = 0 a = g t = t

Using s = ut + 0.5at^2

t^2 = 2/g * h

Plot t^2 against h, and draw a line of best fit.

g = 2/m

What safety precautions should you use in determining the acceleration of a freely falling object, using an electromagnet?

If dropping from a table, clamp the electromagnet stand to the table to prevent it toppling over. (correct)

Be aware of the falling ball, use a tray to capture the ball at the bottom. (correct)

Small currents are used in the circuit, so there is no danger of electric shock. (correct)

All of the above.

What are the possible errors in the method to determine the acceleration of a freely falling object, using an electromagnet?

Small t values, use a larger distance to reduce uncertainty. Signup and view all the answers

Describe the method to determine the electrical resistivity of a material.

<ol> <li>At various points along the wire, measure the diameter, d. Repeat at 90-degree angles at the same point to get about 6 readings and find the average. Then, calculate the cross-sectional area, A.</li> <li>Connect the circuit as shown in the diagram.</li> <li>At 10 cm intervals from the crocodile clips, touch the wire with the probe and record the voltage, v, and current, I, readings on the voltmeter and ammeter.</li> <li>Calculate resistance R as V/I.</li> <li>Measure the length of the wire, L, from one crocodile clip along the wire and record corresponding values of R.</li> </ol> Signup and view all the answers

How do you analyse the results to determine the electrical resistivity of a material?

Plot R against L and draw a line of best fit with the equation R = p/A * L. Calculate the resistivity p = gradient * A. Signup and view all the answers

What safety precautions should you use in determining the electrical resistivity of a material?

Small voltage used so little danger of electric shock. Signup and view all the answers

Evaluate the possible errors in determining the electrical resistivity of a material.

If there is a highly varying voltage/current readings, remove the power supply, voltmeter, ammeter, and replace with an ohm meter (connect clips/probe directly to it). Signup and view all the answers

Describe the method to determine the emf and internal resistance of an electrical cell.

<ol> <li>Set up the apparatus as shown in the diagram.</li> <li>Measure the PD across the terminals Vt using the voltmeter.</li> <li>Vary the current in the circuit by changing the value of the load resistance, R, using the variable resistor, and measure the pd for several values of I.</li> <li>Repeat the process several times and find the average Vt and I.</li> </ol> Signup and view all the answers

Describe how to analyse the results from determining the emf and internal resistance of an electrical cell.

Plot a graph of Vt against I. Draw a line of best fit with the equation Vt = ℰ - Ir. The gradient is the negative internal resistance -r. The y-intercept is ℰ. Signup and view all the answers

What safety precautions should you use for determining the emf and internal resistance of an electrical cell?

Low pd so no danger of shock. Signup and view all the answers

Evaluate any possible errors in determining the emf and internal resistance of an electrical cell?

Keep the temperature constant by opening the switch between readings to prevent current flow in between each trial. Signup and view all the answers

Describe the method to determine the viscosity of a liquid.

<ol> <li>Zero a mass balance with a 250 cm3 measuring cylinder on top.</li> <li>Pour washing up liquid up to the 200 cm3 mark. Record the mass and determine the density of the liquid.</li> <li>Measure the mass of the ball bearing using a top pan balance.</li> <li>Measure the diameter of the ball bearing with a micrometer (different positions and take the average). Then, calculate the volume of the ball.</li> <li>Calculate the density of the ball bearing.</li> <li>Place elastic bands along the measuring cylinder 10 cm apart, measured with a ruler.</li> <li>Drop the ball into the cylinder.</li> <li>Start the stopwatch when the ball touches the top of the washing up liquid. Lap when the bottom of the ball passes a rubber band.</li> <li>Record these two times, t1 and t2.</li> <li>Repeat two more times with the same radius sphere, and then with the same mass but varying radii.</li> <li>For each radius, find the average t1 and t2, calculate the velocities v1 and v2, and average to find Vavg for each radius.</li> </ol> Signup and view all the answers

How do you analyze the results to determine the viscosity of a liquid?

For each radius, where ps is the density of the ball bearing and pl is the density of the liquid, find the viscosity η: η = 2(ps - pl)g / 9vavg Averages the viscosity values to find the mean viscosity. Signup and view all the answers

What safety precautions should be used for determining the viscosity of a liquid?

Spilled liquid can make it easier to slip, so mop up spills. Signup and view all the answers

Evaluate possible errors in determining the viscosity of a liquid.

Keep the temperature roughly the same as it may change the viscosity of the liquid. Signup and view all the answers

Describe the experiment to determine the speed of sound in air.

<ol> <li>Set the time base on the oscilloscope to 100 ms/cm and the y-Gain to 0.1 volts/cm.</li> <li>Connect the microphone to the input on the oscilloscope, activate the second beam mode.</li> <li>Place the microphone in front of the speaker and set the signal generator to 1000 Hz.</li> <li>Place a meter ruler between the signal generator and the microphone.</li> <li>Move the microphone away from the loudspeaker until the microphone's wave has moved one full wavelength along the signal generator's wave, so the peaks and troughs line up.</li> <li>Measure the distance using the meter ruler as one wavelength.</li> <li>Keep moving the microphone back and recording the distance at which the traces line up until 1 meter is reached.</li> <li>Convert the measured distances to record the length of one complete wavelength.</li> <li>Find the mean wavelength.</li> <li>On the oscilloscope, find the time period (number of squares for 1 wavelength * timebase) then invert to find the actual frequency being produced.</li> <li>Vary the frequency on the signal generator to 2000 Hz and 3000 Hz and repeat the procedure as above.</li> <li>Calculate the speed of sound at each frequency using v = f * wavelength, and then calculate the mean speed of sound.</li> </ol> Signup and view all the answers

Describe the safety precautions in determining the speed of sound in air.

Hearing protection used as high-frequency sound can be painful to listen to for long periods. Signup and view all the answers

Evaluate possible errors in determining the speed of sound in air.

Changing the time base until only one wavelength is shown reduces uncertainty in measurements. Signup and view all the answers

What are the safety precautions in investigating the factor affecting the frequency of a vibrating string?

No major hazards - string is elastic, so it won't snap easily, low masses used, the pulley is firmly attached to the bench. Signup and view all the answers

Evaluate any possible errors in investigating the factor affecting the frequency of a vibrating string.

Using an oscilloscope overcomes the uncertainty in the signal generator. Signup and view all the answers

Describe how to determine the wavelength of light using the double-slit experiment.

<ol> <li>Shine monochromatic light (same wavelength) through two slits to produce two coherent wave sources.</li> <li>The coherent waves will interfere as they overlap. Points of constructive interference form bright fringes on the screen, and points of destructive interference form dark fringes on the screen.</li> <li>Measure the slit to screen distance, D, in meters.</li> <li>Measure the slit distance, a, in meters.</li> <li>Measure the fringe separation, x.</li> <li>Calculate the wavelength as follows: Wavelength = ax/D</li> </ol> Signup and view all the answers

Why must you use monochromatic light in the double-slit experiment and small slits?

If you use two sources, the two waves will not be coherent. Slits should be small enough to cause diffraction of light and close enough to allow interference. Signup and view all the answers

Describe how to investigate the change in momentum.

<ol> <li>Determine the mass of the trolley using a mass balance.</li> <li>Place the trolley on a frictionless track.</li> <li>Attach a force sensor to the trolley.</li> <li>Using a motion sensor, measure the initial velocity of the trolley.</li> <li>Apply a constant force to the trolley using a spring or a weight, recording the force applied using the force sensor.</li> <li>Measure the final velocity of the trolley using the motion sensor after the force has been applied.</li> <li>Calculate the initial momentum of the trolley (pi = mv) and the final momentum of the trolley (pf = mv).</li> <li>Calculate the change in momentum (Δp = pf - pi).</li> <li>Compare the change in momentum to the impulse of the force (J = F*Δt) applied to the trolley.</li> </ol> Signup and view all the answers

Describe how to use ICT to analyze collisions between small spheres.

<ol> <li>Record the masses, m, of two spheres using a mass balance, then place them on a level tabletop.</li> <li>Position two meter rulers perpendicular to each other using a set square.</li> <li>Position a video camera above the tabletop and start camera recording.</li> <li>Roll one sphere towards the stationary sphere and allow them to collide and roll.</li> <li>Stop recording when both spheres come to rest.</li> <li>Use video analysis software to go through each frame of the video, use the rulers to calculate the distance traveled and calculate the time between each frame.</li> <li>Use the components to find the initial and final velocities of the spheres.</li> <li>Use velocities to show momentum is conserved.</li> </ol> Signup and view all the answers

Evaluate possible errors in analyzing collisions between small spheres.

Uncertainty in velocities comes from half the range of repeat readings. Signup and view all the answers

Describe how to analyse the PD across a charging and discharging capacitor.

For Charging: <ol> <li>Set up a circuit with a DC power supply and a high resistance resistor.</li> <li>Close the switch to the charging position and start the timer.</li> <li>Record the PD and current every 10s.</li> <li>Repeat the process three times and calculate the mean V and I.</li> <li>Plot a graph of current against time and PD against time.</li> </ol> For Discharging: The same method just move the switch the discharging position. Signup and view all the answers

What are the safety precautions in analyzing the PD across charging/discharging capacitors?

Ensure that the capacitor is connected the right way to prevent it from exploding. Signup and view all the answers

Evaluate possible errors in analyzing the PD across a charging/discharging capacitor.

Increasing the circuit resistance causes the capacitor to discharge slower, measuring a larger value for time reduces percentage uncertainty (and the effect of reaction time). Signup and view all the answers

Describe the method to calibrate a thermistor in a potential divider circuit as a thermostat.

<ol> <li>Connect the thermistor (R1) and a fixed resistor (R2) in a potential divider circuit, with a voltmeter connected across the thermistor.</li> <li>Place the thermistor in a beaker of water.</li> <li>Heat the water using a Bunsen burner and record the temperature of the water using a thermometer, and the voltage across the thermistor using the voltmeter.</li> <li>Repeat steps 2 and 3 for a range of temperatures, ensuring the water is well-stirred and the temperature is stable before each reading.</li> <li>Plot a graph of the voltage across the thermistor against the temperature of the water.</li> <li>Using the graph, determine the voltage at which the thermistor is to be used as a switch for the thermostat (this is the set point temperature).</li> <li>Connect the output of the potential divider to a comparator circuit.</li> <li>Set the comparator circuit to trigger at the predetermined voltage (set point temperature).</li> <li>Connect the comparator circuit to a relay or transistor switch that controls the heating element or cooling system for the thermostat.</li> </ol> Signup and view all the answers

What are the safety precautions in calibrating a thermistor in a potential divider circuit as a thermostat?

Boiling water/Bunsen burner includes a risk of scalds and burns, so do not handle the beaker when hot. Signup and view all the answers

Describe how to determine the specific latent heat of a solid.

<ol> <li>Measure the mass, m, of the container.</li> <li>Add a known mass of ice, mi, and record the initial temperature of the ice.</li> <li>Measure the mass of the container and ice, mci.</li> <li>Pour a measured volume of water, mw, into the container and record the initial temperature of the water.</li> <li>Stir well and record the final stable temperature of the mixture, tf, once all the ice has melted.</li> <li>Calculate the mass of the water, mwi (mwi = mci - mc)</li> <li>Calculate the heat gained by the water ( Qw = mwic(tf - ti,w)).</li> <li>Calculate the amount of heat lost by the ice, Qice (Qice = mi*Lf), where Lf is the specific latent heat of fusion.</li> <li>Assuming no heat losses, Qw = Qice, and the equation can be rearranged to find Lf (Lf = Qw/mi)</li> </ol> Signup and view all the answers

Evaluate possible errors in determining the specific latent heat of a solid.

Uncertainty is +/- 1 degree (uncertainty in each temperature measurement is +/- 0.5 degrees). Signup and view all the answers

Describe how to investigate the adsorption of gamma radiation by lead.

<ol> <li>Set up a Geiger-Muller tube connected to a ratemeter or scaler with a suitable counter.</li> <li>Place the gamma source (e.g., Cobalt-60) at a certain distance from the GM tube, ensuring the source is shielded when not in use.</li> <li>Record the background count rate with the source absent.</li> <li>Place a sheet of lead of known thickness (e.g., 1 mm) between the source and the GM tube and record the count rate.</li> <li>Repeat step 4 for different thicknesses of lead, increasing the thickness incrementally (e.g., 2 mm, 3 mm, 4 mm).</li> <li>Plot a graph of count rate against lead thickness. 7. To obtain a clearer relationship between the count rate and lead thickness, the natural logarithm of the count rate can be plotted against the thickness of lead. This should produce a straight line with a negative gradient (linear relationship).</li> </ol> Signup and view all the answers

What are the safety precautions in the investigating the adsorption of gamma radiation?

Gamma source - reduce exposure time by keeping it in a lead box when not in use, handle with tongs, don't point it at anyone else, and keep a distance. Signup and view all the answers

Evaluate possible errors in the investigation of the adsorption of gamma radiation by lead.

Aluminum removes alpha and beta radiation from the counts, so only gamma is recorded on the 0 count. Signup and view all the answers

Describe how to determine the value of an unknown mass using the resonant frequencies of the oscillation of known masses.

<ol> <li>Hang a spring vertically and attach a known mass, m1.</li> <li>Pull the mass down slightly and release it, allowing the mass to oscillate.</li> <li>Measure the time taken for 10 oscillations and divide by 10 to determine the period of oscillation, T.</li> <li>Calculate the resonant frequency, f = 1/T.</li> <li>Repeat steps 2-4 for a range of known masses, m2 to mn.</li> <li>Plot a graph of resonant frequency (f) against mass (m).</li> <li>Attach the unknown mass to the spring and repeat steps 2-4. Determine the resonant frequency of the unknown mass from the graph.</li> <li>Use the graph to determine the mass (m) that corresponds to the resonant frequency of the unknown mass.</li> </ol> Signup and view all the answers

Evaluate the possible errors in determining the value of an unknown mass using the resonant frequencies of the oscillation of known masses.

Finding time for 10 oscillations then dividing by 10 reduces the percentage uncertainty on each time. Signup and view all the answers

Study Notes

Determining Acceleration of Freely Falling Object

Method: Break electromagnet connection, start timer, measure distance fallen (h), record time (t), repeat three times, average, vary h and record corresponding t values.
Analysis: Use equation s = ut + 0.5at² (where s = h, u = 0, a = g, t = recorded time). Plot t² against h, find gradient (2/g). Calculate g.
Safety Precautions: Clamp electromagnet stand to prevent toppling, use tray to catch falling ball, use small current.
Possible Errors: Small t values (use larger h), time delay due to residual magnetism, air resistance (use smaller, heavier ball).

Determining Electrical Resistivity

Method: Measure wire diameter (d) at multiple points, calculate cross-sectional area (A), connect circuit, record voltage (V) and current (I) at 10cm intervals, calculate resistance (R = V/I), measure wire length (L).
Analysis: Plot R against L, find gradient (p/A), calculate resistivity (p = gradient * A).
Safety Precautions: Low voltage, avoid touching wire directly when warm.
Possible Errors: Variable voltage/current readings (use ohmmeter), uncertainty in micrometre (double uncertainty), poor connections, wire deformation when using high resistance values, lack of straight wire, wire heating.

Determining EMF and Internal Resistance

Method: Set up circuit with voltmeter and variable resistor, measure PD (V_t) across terminals, vary load resistance (R), measure current (I) corresponding to each R. Find average V_t and I
Analysis: Plot V_t against I, draw line and find equation (V_t = ℰ - Ir). Gradient = -r (internal resistance), y-intercept = ℰ(electromotive force).
Safety Precautions: Low voltage, handle variable resistor with care.
Possible Errors: Keep temperature constant by opening switch between readings, use multimeter for fluctuating readings.

Determining Viscosity of a Liquid

Method: Zero mass balance, measure washing up liquid volume (200 cm³) and mass, calculate liquid density. Measure ball bearing mass, diameter (multiple readings), find volume. Calculate ball bearing density. Place elastic bands at 10cm intervals on measuring cylinder, drop ball. Record times t1 and t2 (when ball passes bands). Repeat with same radius and mass but varying radii. Find average t1, t2, calculate velocities v1 and v2, and average velocity.
Analysis: Viscosity (n) = 2(p_s−p_l)g /9 v_avg.
Safety Precautions: Mop up spills, use gloves if needed, wear goggles.
Possible Errors: Constant temperature, ensure ball reaches terminal velocity, reduce uncertainty in time with electronic timing devices, ensure no collisions during fall, ensure laminar flow.

Determining Speed of Sound in Air

Method: Set oscilloscope timebase, y-gain, connect microphone to oscilloscope, place microphone in front of speaker, set signal generator to frequency, move microphone until wave peaks align. Record distance, repeat for different distances, find mean wavelength, determine time period from oscilloscope. Calculate speed (v = f * wavelength).
Safety Precautions: Use hearing protection.
Possible Errors: Timebase settings, signal generators frequency, calibration of oscilloscope.

Investigating Factors Affecting Frequency of a Vibrating String

Method (Tension): Keep length constant. Vary tension by changing hanging mass, measure fundamental frequency(repeating process multiple times).
Method (Mass per unit length, μ): Keep tension constant. Vary μ by using different strings. Measure fundemental frequency
Method (Length): Keep tension and μ constant. Vary length. Measure fundamental frequency (repeating process multiple times).
Analysis: Analyze data to find relationships between frequency, tension, or length and mass per unit length.
Safety Precautions: Low masses, securely attached pulley, no major hazards.
Possible Errors: Oscilloscope timebase setting, signal generator frequency accuracy.

Determining Wavelength of Light (Double-Slit Experiment)

Method: Shine monochromatic light through two slits to produce coherent waves. Measure slit to screen distance (D), slit separation (a), fringe separation (x). Calculate wavelength (λ = ax/D).
Safety Precautions: None explicitly mentioned.
Possible Errors: Monochromatic light source, small slit size, fringe separation measurements.

Determining Wavelength of light (Diffraction Grating)

Method: Shine light through a diffraction grating. Measure the distances, and the angle of the light as it diffracts.
Safety Precautions: None explicitly mentioned.
Possible Errors: Measurement accuracy, grating quality, light source.

Investigating Change in Momentum

Method: Measure masses, position two meter rulers perpendicularly on table. Use video camera to record collision. Use video analysis software to calculate initial and final velocities, compare momentum.
Safety Precautions: None explicitly mentioned
Possible Errors: Uncertainty in velocity measurements, effects of friction.

Analysing PD Across Charging/Discharging Capacitor

Method (Charging): Set up circuit with a DC power supply, resistor. Measure PD across capacitor and current over time.
Method (Discharging): Same as charging, swap switch to discharge.
Analysis: Plot graphs, and interpret by using the relevant equations in the circuit.
Safety Precautions: Appropriate voltages (careful with capacitors), avoid explosion.
Possible Errors: Circuit resistance, reaction time, temperature consistency

Determining Specific Latent Heat of a Solid

Method: Use crushed ice and a thermometer and stirrer in a beaker to record temperature. Measure the mass of the ice, and heat the water in a bunsen to a higher temperature. Mix the two and record the time taken.
Analysis: Use the mass of the ice and the final temperature to calculate specific latent heat.
Safety Precautions: Ensure ice is melting, insulate the container when needed.
Possible Errors: Heat from the surrounding environment, less accurate measurements from the water as it is less visible.

Investigating Relationship Between Pressure and Volume of a Gas

Method: Maintain a constant temperature. Change volume of gas, measure pressure.
Safety Precautions: Prevent temperature changes, measure the excess pressure.
Possible Errors: Temperature is not constant for this experiment, measurement of pressure and volume.

Investigating Adsorption of Gamma Radiation by Lead

Method: Use a Gamma source, lead absorbers. Measure count rate at given thicknesses of lead.
Safety Precautions: Use tongs, wear appropriate PPE, stay behind lead boxes.
Possible Errors: Random decay, background radiation levels, measuring thicknesses correctly.

Determining Unknown Mass Using Resonant Frequencies

Method: Use an oscillating mass system. Measure the resonant frequency, and time.
Safety Precautions: None explicitly mentioned.
Possible Errors: Measuring the time taken, making the oscillating mass system repeatable.

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Description

This quiz covers two essential physics experiments: determining the acceleration of freely falling objects and electrical resistivity of materials. It focuses on methodologies, analysis techniques, safety precautions, and potential errors related to these experiments. Prepare to test your understanding of key concepts in mechanics and electricity.