Measuring Instruments for Experiments Flashcards
time
Stopwatch, light gate
Distance/length (>5 cm)
ruler
Distance/length (1cm < x < 4cm)
Vernier scale/Vernier calliper
Distance/length (< 1cm)
micrometer
Internal diameters
vernier caliper (inner jaws)
Velocity (measure)
Time with stopwatch, distance with ruler, then v = s/t.
OR
Interrupting time with light gate, length of interrupting card (s) with ruler, then v = s/t
Velocity (change)
Roll the object down a slope at variable angles
OR
Use a compressed spring where you can measure the deformation and use conservation of energy
Acceleration (measure)
Single light gate with double interrupting card. The light gate provide t_1 and t_2. You need to measure the length of the double interrupting card (s) then use a = [(s/t_1) - (s/t_2)] / (t1 - t2)
OR
Two light gates with a single interrupting card to measure the velocity at each gate. The system also provides the time between light gates so that DeltaV/Deltat can be calculated.
Force
Newton meter
OR
Often from mass as F = m*g
Mass
Top-pan balance
Energy
Measure time with stopwatch and if power is not given, measure current with ammeter and voltage with voltmeter, then E = Pt, P = IV
Voltage (change)
Use battery with variable resistor/potentiometer
Resistance of component
Measure I with ammeter, V with voltmeter, then use V = I*R
Power
Measure I with ammeter, V with voltmeter, then use P = I*V
Wavelength (measure)
See π in stellar spectra (measure) below
Frequency of sound wave (measure)
Microphone + oscilloscope. The oscilloscope gives T, then use f = 1/T
Frequency of sound wave (change)
Use a signal generator + loudspeaker
Amplitude of sound wave (change)
Use a signal generator and change the voltage + loudspeaker
Frequency of an oscillating object (measure)
Measure time periods across many oscillations, divide by the number of oscillation to find the time period, then use f = 1/T
Frequency of a forced spring mass system oscillating in SHM (change)
Use a signal generator + vibration generator
Wave speed v (change)
Change the medium
Wave speed v (measure) in water
Use a ripple tank. Produce a ripple with a dipper that propagates in the water. Measure the distance (s) travelled with a ruler and measure the time taken (t) to travel that distance. Then use v = s/t.
Use a ripple tank. Connect the dipper to a vibration generator and the vibration generator to a signal generator. Change the frequency of the signal generator (f), that will change the frequency of the wave (f). Immerse a ruler in the ripple tank and measure with it the wavelength of the wave. Measure across multiple wavelengths, then divide by the number of wavelengths. You can determine the frequency of the wave (f) by connecting an oscilloscope in parallel to the signal generator (remember f=1/T). Finally use: v = π*f.
Wave speed v (measure) in chords/strings
Attach the string to a vibration generator and the vibration generator to a signal generator. Change the frequency of the signal generator (f), that will change the frequency of the wave (f). You can measure this frequency by connecting an oscilloscope to the signal generator
(remember f = 1/T). Measure distance between multiple nodes with ruler, then divide by number of nodes. The distance N-N is π/2. Finally use: v = π*f.
Wave speed v (measure) in air column
Immerse an empty cylinder in water. With a tuning fork, create a sound wave. With an oscilloscope check the profile of the wave. It must be a pure sinusoidal wave. Work out the frequency from the displacement-time graph shown on the oscilloscope. Now hit the tuning fork close to the open end of the tube and raise the cylinder away from the water level until the sound gets the loudest. The length of the air in the tube is equal to π/4. Use the wave equation c = π*f to work out the speed of sound in air, c.
Measure the speed or kinetic energy of an electron
Decelerate the electron through two parallel plates (uniform electric field). The plates are also connected to an ammeter that can detect a current if the electron arrives at the negative plate. Increase the voltage across the plates until the current on the ammeter reaches zero. Then use eV = Β½ mv^2
π in stellar spectra (measure)
Let light pass through a diffraction grating. Identify the central maxima and the next orders on both sides. Measure the distance, D, between the screen and the grating. Measure the distance, x, between the position of the central order and that of the nth-order. Use tan(πΉ) = x/D to work out πΉ. Use dsin(πΉ) = nπ to workout π.
Radial velocity of stars (measure)
Or recessional velocity of galaxies (measure)
Use a gas-discharge lamp and a diffraction grating to produce an emission spectrum of a hot gas. Measure the wavelength as per the method above (π_lab). Measure the wavelength for the same line in the stellar spectra (π_star).
Calculate the change in the wavelength as ππ = π_star - π_lab. Then use the Doppler shift formula to work out the speed v of the star/galaxy (ππ/π_lab = v/c).
Plankβs constant (measure)
Use the equation
hc/π = eV. This needs to be rearrange as V=(hc/e)(1/π). Plot V on the y axis, 1/π on the x axis.
h = grade/c
Change wavelength by changing LED and measure wavelength with diffraction grating. Measure V as the threshold voltage at which the LED start lighting up. The LED needs to be in a circuit with a power supply and a variable resistor. This will allow to change the voltage across the LED. Measure voltage with voltmeter. Work in a darkened room.
Time constant in capacitors (measure)
Discharging. Close/open switch, measure time with stopwatch and voltage with voltmeter in parallel to capacitor (or use data logger with voltmeter sensor to measure both). Linearize equation V = V_0e^-t/RC by plotting ln V vs. t, gradient is -1/RC.
Charging. Open/close switch, measure time with stopwatch and voltage with voltmeter in parallel to capacitor (or use data logger with voltmeter sensor to measure both). Linearize equation V = V_0(1-e^-t/RC) by plotting ln(1-V/V_0) vs. t, gradient is -1/RC.
Magnetic flux density (B) (measure)
Use a search coil. This only works if you are trying to measure an AC magnetic field.
Use an Hall probe. This works well also for DC magnetic fields.
Decay constant () of radioactive source (measure)
Use a Geiger-Muller (GM) tube connected to a counter. This will allow you to measure the number of decay events (C) in a certain amount of time. Measure time with the stopwatch. Increase time until you have %U <= 1%. Remember in counting U = C^1/2. Use the equation C=C_0*e^-t, linearize it and plot plotting ln C vs. t, gradient is -π.
Half life (t_1/2) of radioactive source (measure)
Determine π as in previous, then t_1/2 = ln 2/π
Half thickness (x_1/2) (measure)
Use a Geiger-Muller (GM) tube connected to a counter. This will allow you to measure the number of decay events (C) in a certain amount of time. Measure time with the stopwatch. Increase time until you have
%U <= 1%. Remember in counting U = C^1/2. Change different thicknesses of absorbing material. Measure thickness with a micrometer. Use the equation C = C_0e^-mux, linearize it and plot ln C vs. x, gradient is -mu.
Displacement time graph for an object doing SHM
Use a motion sensor that emits ultrasound and measure the time it takes for ultrasound to be reflected back. Connect a reflecting surface to the object doing SHM.
Freeze the motion of something vibrating at a frequency f
Use a stroboscope. Vary the frequency of the stroboscope until the movement is frozen. Then read the frequency f from the stroboscope.
Speed of blood in veins
Send an ultrasound of known frequency f at an angle πΉ from the blood vessel. Measure the frequency of the x-rays that is reflected back. Use the Equation: Deltaf/f = 2cos(πΉ)v/c
Temperature (measure)
Use a thermometer.
To improve accuracy:
- In liquids: be sure to stir liquid and wait until thermal equilibrium is reached.
- In solids: use some liquid drops to increase thermal conductivity
- read at eye level to avoid parallax
Temperature (change)
- Use an electric immersion heater
- Add some water at different temperatures
