Measuring Instruments for Experiments

Question 1

time

Answer 1

Stopwatch, light gate

Question 2

Distance/length (>5 cm)

Answer 2

ruler

Question 3

Distance/length (1cm < x < 4cm)

Answer 3

Vernier scale/Vernier calliper

Question 4

Distance/length (< 1cm)

Answer 4

micrometer

Question 5

Internal diameters

Answer 5

vernier caliper (inner jaws)

Question 6

Velocity (measure)

Answer 6

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

Question 7

Velocity (change)

Answer 7

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

Question 8

Acceleration (measure)

Answer 8

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.

Question 9

Force

Answer 9

Newton meter
OR
Often from mass as F = m*g

Question 10

Mass

Answer 10

Top-pan balance

Question 11

Energy

Answer 11

Measure time with stopwatch and if power is not given, measure current with ammeter and voltage with voltmeter, then E = Pt, P = IV

Question 12

Voltage (change)

Answer 12

Use battery with variable resistor/potentiometer

Question 13

Resistance of component

Answer 13

Measure I with ammeter, V with voltmeter, then use V = I*R

Question 14

Power

Answer 14

Measure I with ammeter, V with voltmeter, then use P = I*V

Question 15

Wavelength (measure)

Answer 15

See 𝛌 in stellar spectra (measure) below

Question 16

Frequency of sound wave (measure)

Answer 16

Microphone + oscilloscope. The oscilloscope gives T, then use f = 1/T

Question 17

Frequency of sound wave (change)

Answer 17

Use a signal generator + loudspeaker

Question 18

Amplitude of sound wave (change)

Answer 18

Use a signal generator and change the voltage + loudspeaker

Question 19

Frequency of an oscillating object (measure)

Answer 19

Measure time periods across many oscillations, divide by the number of oscillation to find the time period, then use f = 1/T

Question 20

Frequency of a forced spring mass system oscillating in SHM (change)

Answer 20

Use a signal generator + vibration generator

Question 21

Wave speed v (change)

Answer 21

Change the medium

Question 22

Wave speed v (measure) in water

Answer 22

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 = 𝛌*f.

Question 23

Wave speed v (measure) in chords/strings

Answer 23

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 𝛌/2. Finally use: v = 𝛌*f.

Question 24

Wave speed v (measure) in air column

Answer 24

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 𝛌/4. Use the wave equation c = 𝛌*f to work out the speed of sound in air, c.

Question 25

Measure the speed or kinetic energy of an electron

Answer 25

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 = ½ mv^2

Question 26

𝛌 in stellar spectra (measure)

Answer 26

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(𝚹) = x/D to work out 𝚹. Use dsin(𝚹) = n𝛌 to workout 𝛌.

Question 27

Radial velocity of stars (measure)
Or recessional velocity of galaxies (measure)

Answer 27

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 (𝛌_lab). Measure the wavelength for the same line in the stellar spectra (𝛌_star).
Calculate the change in the wavelength as 𝜟𝛌 = 𝛌_star - 𝛌_lab. Then use the Doppler shift formula to work out the speed v of the star/galaxy (𝜟𝛌/𝛌_lab = v/c).

Question 28

Plank’s constant (measure)

Answer 28

Use the equation
hc/𝛌 = eV. This needs to be rearrange as V=(hc/e)(1/𝛌). Plot V on the y axis, 1/𝛌 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.

Question 29

Time constant in capacitors (measure)

Answer 29

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.

Question 30

Magnetic flux density (B) (measure)

Answer 30

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.

Question 31

Decay constant () of radioactive source (measure)

Answer 31

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 -𝛌.

Question 32

Half life (t_1/2) of radioactive source (measure)

Answer 32

Determine 𝛌 as in previous, then t_1/2 = ln 2/𝛌

Question 33

Half thickness (x_1/2) (measure)

Answer 33

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.

Question 34

Displacement time graph for an object doing SHM

Answer 34

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.

Question 35

Freeze the motion of something vibrating at a frequency f

Answer 35

Use a stroboscope. Vary the frequency of the stroboscope until the movement is frozen. Then read the frequency f from the stroboscope.

Question 36

Speed of blood in veins

Answer 36

Send an ultrasound of known frequency f at an angle 𝚹 from the blood vessel. Measure the frequency of the x-rays that is reflected back. Use the Equation: Deltaf/f = 2cos(𝚹)v/c

Question 37

Temperature (measure)

Answer 37

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

Question 38

Temperature (change)

Answer 38

• Use an electric immersion heater
• Add some water at different temperatures