Foundations of Physics Flashcards
What are physical quantities?
They consist of a numerical magnitude and a unit - to represent a physical quantity, it must contain both a numerical value and the units its measured in
What is the estimation for the diameter of an atom?
10^-10 m
What is the estimation for the wavelength of UV light?
10 nm
What is the estimation for the distance between the earth and the sun (1AU)?
1.5 x 10^8 m
What is the estimation for mass of a hydrogen atom?
10^-27 kg
What is the estimation for the mass of an adult human?
70kg
What is the estimation for the mass of a car?
1000 kg
What is the estimation for seconds in a year?
3 x 10^7 s
What is the estimation for the power of a lightbulb?
60 W
What is the estimation for atmospheric pressure?
1 x 10^5 Pa
What are the 7 SI base units?
- Kilogram, kg (mass)
- Metre, m (length)
- Second, s (time)
- Ampere, A (current)
- Kelvin, K (temperature)
- Mole, mol (temperature)
- Candela, cd (luminosity
What are derived units?
Units of a quantity that are based solely on the 7 SI base units
What is the derived SI base unit of the newton?
kg ms^-2
What is the derived SI base unit of the joule?
kg m^2 s^-2
What is the derived SI base unit of the pascal?
kg m^-1 s^-2
What is homogeneity?
When something is all the same or of the same kind
How do you check the homogeneity of a physical equation?
- Check the units on both sides of an equation
- Determine if they are equal
- If they do not match, the equation will need to be adjusted
What is the order of prefixes?
POSITIVE
kilo, mega, giga, tera, peta
NEGATIVE
milli, micro, nano, pico, femto
What is the centi prefix?
10^-2
What is the micro prefix?
10 ^-6
What is the general convention for tables?
- Independent variable in the left column
- Dependant variable in the right column
What is the general convention for graphs?
- Independent variable plotted on the x-axis
- Dependant variable plotted on the y-axis
What is uncertainty?
An estimate of the difference between a measurement reading and the true value
What leads to uncertainty?
Errors
What are the 2 main types of error?
Random and systematic
What is random error?
Error that causes unpredictable fluctuations in an instruments reading as a result of uncontrollable factors, such as environment
How can you reduce random error?
Take repeat measurements several times and calculate an average from them
What is systematic error?
Error that arises from the use of faulty instruments or from flaws in the experimental method. This type of error is repeated consistently every time the instrument is used or the method is followed, which affects the accuracy of all readings obtained
How can you reduce systematic error?
- Instruments should be recalibrated or different instruments should be used
- Corrections and adjustments should be made to the technique
What is a zero error?
A type of systematic error which occurs when an instrument gives a reading when the true reading is 0
What are precise measurements?
Ones in which there is very little spread about the mean value
What are accurate measurements?
Measurements close to the true value
What is absolute uncertainty?
Where uncertainty is given as a fixed quantity
What is percentage uncertainty?
Where uncertainty is given as a percentage of the measurement
What is the calculation for percentage uncertainty?
Percentage uncertainty = (uncertainty/ measured value) x 100
How do you calculate uncertainty in a reading?
+ or - half the smallest division
How do you calculate uncertainty in repeated data?
Half the range
How do you calculate the combined uncertainty when adding/ subtracting data?
Add the absolute uncertainties
How do you calculate the combined uncertainty when multiplying/ dividing data?
Add the percentage uncertainties
How do you calculate the combined uncertainty when raising data to a power?
Multiply the percentage uncertainty by the power - multiply this by the value you are finding the uncertainty of to get the absolute uncertainty
What are error bars?
Plotted on graphs to show the absolute uncertainty of values plotted
How do you calculate the uncertainty in a gradient?
Draw 2 lines of best fit:
- Line of best fit = passes as close to the points as possible
- Line of worst fit = the steepest or shallowest possible line which fits within all error bars
Percentage gradient = (best gradient - worst gradient) / best gradient x 100
What is the percentage difference equation?
Percentage difference = (measured value - accepted value) / accepted value x 100
The smaller the percentage difference, the _____ accurate the results of the experiment
More
What is a scalar quantity?
A quantity which only has magnitude
What is a vector quantity?
A quantity which has both magnitude and direction
What are examples of scalar quantities?
- Distance
- Speed
- Mass
- Time
- Energy
- Volume
- Density
- Pressure
- Electric charge
- Temperature
What are examples of vector quantities?
- Displacement
- Velocity
- Acceleration
- Force
- Momentum
How can you combine perpendicular vectors that are directed in the same direction?
Add them together
How can you combine perpendicular vectors that are directed in opposite directions?
Take them away from one another - the vector you take away from is the resultants direction
What is the sine rule?
A/ sin a = B/ sin b
What is the cosine rule?
a^2 = b^2 + c^2 - 2bc cos θ
What is the horizontal component of a force?
F cosθ
What is the vertical component of a force?
F sinθ
