Working as a Physicist Flashcards
The principle of ‘homogeneity of units’ means:
Units in any equation must be the same on both sides
State the SI base quantities.
Amount of Substance Current Distance Luminocity Mass Temperature Time
State the SI base units.
Moles (mol) Amperes (A) Meters (m) Candela (cd) Kilograms (kg) Kelvin (K) Seconds (s)
The SI derived unit for momentum is:
kg m s⁻¹
A quantity that has the SI derived unit s⁻¹ is:
Frequency
A quantity that has the SI derived unit kgm⁻³ is:
Density
What are the following conversions?
pN→ nN → μN → mN → N → kN → MN → GN → TN
p x10⁻¹² n x10⁻⁹ μ x10⁻⁶ m x10⁻³ - k x10³ M x10⁶ G x10⁹ T x10¹²
The units for strain are:
No units
A graph with the current on the y-axis and time on the x-axis shows?
The current against time
What does the gradient of a velocity-time graph represent?
Acceleration
∵gradient = Δy / Δx
& velocity (ms⁻¹) / time (s) = acceleration (ms⁻²)
What is the dependent variable on a graph?
y-axis
What is the independent variable on a graph?
x-axis
What does the area under a force-displacement graph represent?
Work Done
∵area = Δy x Δx
& Force x Displacement = Work Done
Why do we have base units?
These provide a source to derive all other units and ensure that research can be easily compared.
What is absolute uncertainty?
The uncertainty in a specific measurement
What is the unit for absolute uncertainty?
It is given in the same units as the original measurement
How is the absolute uncertainty stated?
It is stated after the measurement as ± [number] [unit].
What are three ways to calculate absolute uncertainty?
- half the smallest division on the instrument.
- half of the last significant figure recorded.
- half the range of your repeats.
What is % uncertainty?
It’s how the size of the uncertainty compares to the measurement.
How is the % uncertainty stated?
It is stated after the measurement as ± [number] %
How do you calculate % uncertainty?
(the absolute uncertainty / by the average measurement) x 100
What happens to the uncertainty when you:
1) add/subtract measurements?
2) multiply/divide measurements?
3) raising measurements to a power?
1) add the absolute uncertainties.
2) add the percentage uncertainties.
3) multiply the percentage uncertainty by the power.
