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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.

Your recallNot started
Process

What multiplying factors are represented by the prefixes pico, nano, micro and milli?

Process

Why is the radian not an SI base unit?

Process

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. 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. 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. 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. 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. 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. 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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