Topic 1 Flashcards
Define physical quantity
A quantity that can be measured and consists of a magnitude and a unit
What are SI units?
The International System of Units
Name the 6 SI units
- Metre
- Kilogram
- Second
- Ampere
- Kelvin
- Mole
Define base quantity
Quantities on the basis of which other quantities are expresses
Define derived quantities
Quantities that are expressed in terms of base quantities
Define homogenuous
Quantities on both sides of an equation have the same unit
Homogeneous equation may not be ______ correct but a _______ correct equation is definitely homogeneous
Physically
What are the 9 prefixes, their abbreviations and powers
nano n 10^-9
micro μ 10^-6
milli m 10^-3
centi c 10^-2
deci d 10^-1
kilo k 10^3
mega M 10^6
giga G 10^9
tera T 10^12
Define scalar quantity
Quantities that have magnitude only and no direction
Define vector quantity
Quantities that have both magnitude and direction
Give 7 examples of a scalar quantity
Mass, temperature, energy, distance, speed, density, pressure
Give 6 examples of a vector quantity
Displacement, velocity, weight, acceleration, force, momentum
What is the difference between collinear and coplanar?
Collinear is parallel to the same line and coplanar is parallel to the same plane
Define uncertainty
Estimate of the difference between the reading and the true value of the quantity
Define error
A reason that a measurement might be wrong
Define precision
The smallest change in a value that can be measured by an instrument or an operator. To be precise, repeated measurements of the same thing should be close
Define accuracy
An accurate value of a a measured quantity is one that is close to the true value of the quantity
What is a systematic error?
A factor that causes readings to be different form the true value by a consistent amount each time the reading is made
What is a zero error?
A type of systematic error which occurs when an instrument gives a non-zero reading when the true value of the quantity is 0
How can you get rid of a zero error?
Can be removed by adding or subtracting it from your values
What is a random error?
Causes readings to vary around the mean value in an unpredictable way from one reading to another
How can a random error be reduced?
By repeating and averaging results
How do you find the uncertainty of a single measurement?
Precision of the measurement device (smallest value measured by the device)
How do you find the uncertainty of repeated measurements?
Half the range of the measured values
How do you find the uncertainty of repeated IDENTICAL measurements?
Precision of the measurement device
State the formula for percentage uncertainty
Uncertainty
———————– x 100 (1 s.f.)
Measured value
How to combine uncertainties when adding or subtracting?
Add the absolute uncertainties
How to combine uncertainties when multiplying?
Add the percentage uncertainties
How to combine uncertainties when raising to a power?
Multiplying the percentage uncertainties by the power
Is parallax error systematic or random?
Systematic if you always view the dial from the same angle and random if you view the dial from a random angle each time
Is reaction error systematic or random?
Random error (Reaction time can vary)
Do random errors or systematic errors affect the average?
Only systematic affect the average (bias) and random only affects the variability around the average
What are the sources of random errors? (2)
- Operator systems
- Changes in experimental conditions
Define limit of reading
The smallest graduation of the scale of an instrument
What are the sources of systematic errors? (3)
- Instrumental
- Physical
- Human limitation (device is out of callibration)
How to minimise systematic errors? (2)
- Careful calibration
- Best possible techniques
What is precision affected by and what does it look like on a graph?
Random error
Scattering about straight line
What is accuracy affected by and what does it look like on a graph?
Systematic error
Straight line parallel to best fit
What is an oscilloscope?
A test instrument that allows you to look at the ‘shape’ of electrical signals by displaying a graph of voltage against time
What can the graph on an oscilloscope also be called?
Trace
How is a graph from an oscilloscope drawn?
By a beam of electrons striking the phosphor coating of the screen, making it emit light (green/blue)
- like how a tv picture is produced
How does an oscilloscope work?
They contain a vacuum tube with a cathode at one end to emit electrons and an anode to accelerate them so they move rapidly down the tube to the screen
What are the cathode and the anode in an oscilloscope also called?
Electron gun
What is the purpose of the deflection plates in an oscilloscope?
They deflect the electron beam up/down and left/right
What can the electrons in an oscilloscope also be called?
Cathode rays
How do you obtain a clear and stable trace on an oscilloscope?
Adjust the controls
- Y amplifier (volts/cm) to determine the height of the trace
- Timebase (time/cm) to determine the rate at which the dot sweeps the screen
What is the amplitude?
The maximum voltage reached by the signal
What is the peak-peak voltage?
2 times the amplitude
What is the time period?
The time taken for the signal to complete one cycle
What is the frequency?
Number of cycles per second
OR 1/Time period
Why is the peak-peak voltage read?
It can be read correctly even if the position of 0v is not known
