Edexcel A-Level Physics 9PH0
Working as a Physicist
Mechanics
Electric Circuits
Materials
Waves and Particle Nature of Light
Further Mechanics
Electric and Magnetic Fields
Nuclear and Particle Physics
Thermodynamics
Space
Nuclear Radiation
Gravitational Fields
Oscillations
Working as a Physicist
Unit prefixes, conversion and order-of-magnitude estimates
- 3 things to know
- Papers 1, 2 and 3
Overview
Recall questions on the prefixes from pico to tera, converting to SI before substituting, and making an order-of-magnitude estimate to one significant figure.
What you need to know
Answer each one before you reveal it.
Why is the radian not an SI base unit?
Why should the result of an estimate normally be quoted to one significant figure?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What multiplying factors are represented by the prefixes pico, nano, micro and milli?
Model answer
Pico is 10⁻¹², nano is 10⁻⁹, micro is 10⁻⁶ and milli is 10⁻³.
- 2
What multiplying factors are represented by the prefixes kilo, mega, giga and tera?
Model answer
Kilo is 10³, mega is 10⁶, giga is 10⁹ and tera is 10¹².
- 3
Why is the radian not an SI base unit?
Model answer
An angle in radians is an arc length divided by a radius, so the metres cancel and the angle is a pure number with no unit.
- 4
A car travels at 108 km h⁻¹. What is this speed in m s⁻¹?
Model answer
Dividing by 3.6 gives a speed of 30 m s⁻¹.
- 5
Why must every quantity be converted to SI units before it is substituted into a physics equation?
Model answer
The equations and the constants within them are defined for SI units, so leaving a value in centimetres or grams gives an answer wrong by a power of ten.
- 6
What is an order-of-magnitude estimate?
Model answer
It is a value quoted only to the nearest power of ten, used to judge whether a quantity is of a reasonable size.
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