Module 1: Development of Practical Skills in Physics Flashcards
What is accuracy?
How close a measurement is to the true value.
What is precision?
How close the measurements are to each other.
How can accuracy be increased?
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.
What is a random error?
Random errors are readings scattered about the true value and can be eliminated by averaging.
What is a systematic error?
Systematic errors are constant errors in all measurements and canโt be eliminated by averaging.
When adding quantities A and B, what is the uncertainty?
Uแด + Uส
When multiplying or dividing quantities A and B by each other, what is the percentage uncertainty?
%Uแด + %Uส
When raising a quantity, A, by a power of n, what is the percentage uncertainty?
n(%Uแด)
What is the uncertainty of a range of values?
range/2
What is the uncertainty of the gradient of a line?
(LOBF-LOWF)/2
How do you measure time?
Stopwatch, light gate
How do you measure distance / length (>5 cm)?
Ruler (resolution 1 mm)
How do you measure distance / length (1cm<x< 4cm)?
Vernier scale/vernier caliper (resolution 0.1 mm)
How do you measure distance / length (< 1cm)?
Micrometer (resolution 0.01 mm and below)
How do you measure internal diameters?
Vernier caliper (inner jaws)
How do you measure velocity?
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
How do you measure velocity change?
Roll the object down a slope at variable angles
Use a compressed spring where you can measure the deformation and use conservation of energy
How do you measure acceleration?
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
How do you measure force?
Newton meter
Or
Often from mass as F=mg
How do you measure mass?
Balance / scale
How do you measure energy (electricity)
Measure time with stopwatch and if power is not given, measure current with ammeter and voltage with voltmeter, then E=Pt, P=IV
How do you measure current (DC)?
Ammeter
How do you measure current (AC)?
Ammeter
How do you measure voltage (DC)?
Voltmeter
How do you measure voltage AC?
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
How do you measure change in voltage?
Use battery with variable resistor/potentiometer
How do you measure the resistance of a component?
Measure I with ammeter, V with voltmeter, then use V=IR
How do you measure power?
Measure I with ammeter, V with voltmeter, then use P=IV
How do you measure wavelength?
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(๐น) = x/D to work out theta. Use d sin(๐น) = n ๐ to work out ๐.
How do you measure the frequency of sound wave?
Use a microphone and oscilloscope. The oscilloscope gives T, then use f=1/T
How do you measure the change in frequency of a sound wave?
Use a signal generator and loudspeakers
How do you measure the change in amplitude of sound wave?
Use a signal generator and change voltage and use loudspeakers
How do you measure the frequency of an oscillating object?
Measure time periods across many oscillations, divide by the number of oscillation to find the time period, then use f=1/T
How do you measure the change in the frequency of a forced spring mass system oscillating in SHM?
Use a signal generator + vibration generator
How do you measure the change in wave speed?
Change the medium
How do you measure wave speed 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=f๐
How do you measure wave speed 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 ๐/2.
Finally use:v=f๐.
How do you measure wave speed in an 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 ๐/4. Use the wave equation f =๐c to work out the speed of sound in air, c.
How do you measure the speed or kinetic energy of an electron?
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=ยฝ mv^2
How do you measure Plankโs constant?
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 Planckโs constant by using the equation:
hf = eV - hf_0
2.
Use the equation hc/๐=eV.
This needs to be rearrange as V=hc/๐e. Plot V on the y axis, 1/๐ 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.
How to measure time constant in capacitors?
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
