Physics Edexcel A level Topic 1 Working as a Physicist

What are SI base units?

SI base units are the standard units used to describe physical quantities in physics. (SI stands for international system of units).

What is the SI unit for time?

Seconds

What is the SI unit for temperature?

Kelvin (K)

What is the SI unit for electric current?

Ampere (A)

What is the SI unit for distance (length)?

Metre (m)

What is the SI unit for mass?

Kilogram (kg)

What is the SI unit for luminous intensity?

Candela (cd)

What is the SI unit for chemical mass?

Mole (mol)

How do you convert Celsius to Kelvin?

K = C + 273

What is the SI unit for pressure?

Pascal (Pa)

What is the SI unit for energy?

Joule (J)

What is the SI unit for frequency?

Hertz (Hz)

What is the SI unit for power?

Watt (W)

What is the SI unit for force?

Newton (N)

What is the SI unit for electric charge?

Coulomb (C)

What is the SI unit for electric potential difference?

Volt (V)

What is the SI unit for electric resistance?

Ohm (Ω)

What is the SI unit for magnetic flux density?

Tesla (T)

Nano (n)

10^-9

Micro (μ)

10^-6

Milli (m)

10^-3

Centi (c)

10^-2

Kilo (k)

10^3

Mega (M)

10^6

Giga (G)

10^9

What is standard form used to represent?

Standard form is used to represent large or very small numbers.

What's the format in which standard form numbers are written in?

Standard form numbers are written in the format: A x 10 ^n where A is a number between 0 and 10 and n is how many places to move the decimal point.

How do you convert units?

To convert a smaller unit to a larger unit (eg cm to m), first divide it by the number of smaller units which are needed to make 1 larger unit. To convert from a larger unit to a smaller one, multiply. To convert from a smaller unit to a larger one, divide.

All measurement has an associated uncertainty. What do we call this uncertainty?

Error

What is a measurement model?

A model of a measurement in two parts. One part is the observed value and the other value is the measurement called the true value.

The uncertainty we have about our measurement is called the error. So the model is:

observed value = true value + error

What are the two parts of error in our measurement model made up of?

Random error and Systematic error.

What is a way you could rewrite the measurement model?

Observed value = true value + random error + systematic error

Does the measurement model usually have a positive or negative error in practice?

Positive error

What could an error on a measurement mean for the true value?

It could mean that true value is more or less than the observed value.

What is a systematic error?

An error that follows a set pattern.

e.g

a repeating pattern which is more or less than the true value at the same rate every-time.

Is it hard to avoid a systematic error?

Yes

How can you avoid systematic errors?

You could use measuring equipment to measure a known value.

What is the process called in which you use measuring equipment to measure a known value?

Calibration.

What is a random error?

A random error is an error that follows no set pattern.

A random error could be due to reading the measuring equipment in different ways. The error could be because the measuring equipment bin different ways.

What is a good way to reduce random errors in an experiment?

Doing lots of repeats.

What can we assume about the observed value after a lot of repeats (if there is no systematic error)?

That the observed value is the true value.

What does accuracy mean when describing measurements?

Accuracy is how close a measurement is to the correct value for that measurement.

What does precision mean when describing measurements?

Precision of a measurement system refers to how close to each other the repeated measurements are.

This is independent of the "true" value of the measurement.

What does repeatability mean when describing measurements?

It means that if the experiment was carried about by another person with the same apparatus, that they would get the same results (within random errors).

What does reproducibility mean when describing measurements?

A measurement is reproducible if a different person can perform the same experiment with the same apparatus and get the same results.

What does resolution mean when describing measurements?

The resolution of a measuring equipment describes its maximum precision.

What are the 5 ways you can describe measurements?

• Resolution

• Repeatability

• Reproducability

• Precision

• Accuracy

How is uncertainty shown on a graph?

Error bars

What is order of magnitude?

A power to the base 10 used to quantify and compare size.