CAIE IGCSE Physics One Light-Year Equals 9.5 × 10^15 m

Practise recalling and deriving the metre value of a light-year, then convert astronomical distances between light-years, metres and kilometres.

Exam points

recall that one light-year is 9.5 × 10^15 m, equivalent to 9.5 × 10^12 km
derive the value from distance = light speed × seconds in one year using standard form
multiply or divide by the conversion factor to change stellar and galactic distances between units

[Maximum number: 2]

The Milky Way is the galaxy in which the Solar System is located.

The Milky Way has a diameter that is approximately equal to 100000 light-years.

Determine this distance in kilometres (km).

$9.5 \times 10^{17}(\mathrm{~km})$

A2

(1 light-year =) $9.5 \times 10^{15}(\mathrm{~m})$ OR (1 light-year =) $3 \times 10^{8} \times 365 \times 24 \times 3600$

C1

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6.2.2.2—One light-year is equal to 9.5 × 1015 question 1