Module 1: Development of Practical Skills in Physics

Question 1

What is accuracy?

Answer 1

How close a measurement is to the true value.

Question 2

What is precision?

Answer 2

How close the measurements are to each other.

Question 3

How can accuracy be increased?

Answer 3

Accuracy can be increased by using a measuring instrument with a higher resolution, repeating measurements and calculating a mean, or by measuring a larger quantity to reduce percentage uncertainty.

Question 4

What is a random error?

Answer 4

Random errors are readings scattered about the true value and can be eliminated by averaging.

Question 5

What is a systematic error?

Answer 5

Systematic errors are constant errors in all measurements and can’t be eliminated by averaging.

Question 6

When adding quantities A and B, what is the uncertainty?

Answer 6

Uᴀ + Uʙ

Question 7

When multiplying or dividing quantities A and B by each other, what is the percentage uncertainty?

Answer 7

%Uᴀ + %Uʙ

Question 8

When raising a quantity, A, by a power of n, what is the percentage uncertainty?

Answer 8

n(%Uᴀ)

Question 9

What is the uncertainty of a range of values?

Answer 9

range/2

Question 10

What is the uncertainty of the gradient of a line?

Answer 10

(LOBF-LOWF)/2

Question 11

How do you measure time?

Answer 11

Stopwatch, light gate

Question 12

How do you measure distance / length (>5 cm)?

Answer 12

Ruler (resolution 1 mm)

Question 13

How do you measure distance / length (1cm<x< 4cm)?

Answer 13

Vernier scale/vernier caliper (resolution 0.1 mm)

Question 14

How do you measure distance / length (< 1cm)?

Answer 14

Micrometer (resolution 0.01 mm and below)

Question 15

How do you measure internal diameters?

Answer 15

Vernier caliper (inner jaws)

Question 16

How do you measure velocity?

Answer 16

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 17

How do you measure velocity change?

Answer 17

Roll the object down a slope at variable angles
Use a compressed spring where you can measure the deformation and use conservation of energy

Question 18

How do you measure acceleration?

Answer 18

Single light gate with double interrupting card. The light gate provide t1and t2. You need to measure the length of the double interrupting card (s) then use a = [(s/t1)-(s/t2)] / [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 vt can be calculated

Question 19

How do you measure force?

Answer 19

Newton meter

Or

Often from mass as F=mg

Question 20

How do you measure mass?

Answer 20

Balance / scale

Question 21

How do you measure energy (electricity)

Answer 21

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

Question 22

How do you measure current (DC)?

Answer 22

Ammeter

Question 23

How do you measure current (AC)?

Answer 23

Ammeter

Question 24

How do you measure voltage (DC)?

Answer 24

Voltmeter

Question 25

How do you measure voltage AC?

Answer 25

Voltmeter, but better an oscilloscope. With an oscilloscope measure peak to peak voltage , then divide by 2. Use the number of volts/div to infer the p2p Voltage

Question 26

How do you measure change in voltage?

Answer 26

Use battery with variable resistor/potentiometer

Question 27

How do you measure the resistance of a component?

Answer 27

Measure I with ammeter, V with voltmeter, then use V=IR

Question 28

How do you measure power?

Answer 28

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

Question 29

How do you measure wavelength?

Answer 29

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 theta. Use d sin(𝚹) = n 𝛌 to work out 𝛌.

Question 30

How do you measure the frequency of sound wave?

Answer 30

Use a microphone and oscilloscope. The oscilloscope gives T, then use f=1/T

Question 31

How do you measure the change in frequency of a sound wave?

Answer 31

Use a signal generator and loudspeakers

Question 32

How do you measure the change in amplitude of sound wave?

Answer 32

Use a signal generator and change voltage and use loudspeakers

Question 33

How do you measure the frequency of an oscillating object?

Answer 33

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

Question 34

How do you measure the change in the frequency of a forced spring mass system oscillating in SHM?

Answer 34

Use a signal generator + vibration generator

Question 35

How do you measure the change in wave speed?

Answer 35

Change the medium

Question 36

How do you measure wave speed in water?

Answer 36

1. 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. 2. 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=f𝛌

Question 37

How do you measure wave speed in chords/strings?

Answer 37

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=f𝛌.

Question 38

How do you measure wave speed in an air column?

Answer 38

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 f =𝛌c to work out the speed of sound in air, c.

Question 39

How do you measure the speed or kinetic energy of an electron?

Answer 39

Decelerate the electron through two parallel plates (uniform electric fields). 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 40

How do you measure Plank's constant?

Answer 40

1. In an evacuated glass tube, shine light onto a metal plate. The frequency *f* must be larger than the threshold frequency *f_0 *of that metal. Decelerate the photoelectrons by applying a stopping voltage V across the tube. Vary the applied voltage until no electrons make it to the other end of the tube. Workout the Planck's constant by using the equation: hf = eV - hf_0 2. Use the equation hc/𝛌=eV. This needs to be rearrange as V=hc/𝛌e. Plot V on the y axis, 1/𝛌 on the x axis. h=(gradient)e/c Change wavelength by changing LED and measure wavelength with diffraction grating (see relative box). 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 on the LED. Measure voltage with voltmeter. Work in a darkened room.

Question 41

How to measure time constant in capacitors?

Answer 41

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=V0e-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=V0(1-e-t/RC) by plotting ln (1-V/V0 ) vs. t, gradient is -1/RC