During a survey, a radio dish with a diameter of 12 m takes 25 min to gather the required signal from a particular source. The observatory replaces it with a dish of diameter 20 m, while keeping the receiver and observing conditions unchanged.
For this steady source, the signal collected each minute scales with dish diameter squared. Increasing the duration of an observation by a given factor increases the total signal by the same factor.
What observing time should be used with the new dish to obtain the required signal?
25 min25\ \mathrm{min}25 min
42 min42\ \mathrm{min}42 min
9 min9\ \mathrm{min}9 min
15 min15\ \mathrm{min}15 min
75 exam-style questions on Edexcel GCSE Physics 7.3 Stars, covering 7.3.1 Evolution of stars similar to the Sun, 7.3.2 Evolution of massive stars, and 7.3.3 Observing the Universe. Each one has a worked solution and a mark scheme showing where the marks go.