A GPS satellite develops a fault whereby it moves into an orbit 19 600 km above the Earth's surface and also emits a weak signal whose power is only 19 W. What will be the power per square metre of the signal received on the Earth's surface? Choose the nearest value from the list below. (W/m² represents 'watts per square metre'.)

Select one:

2 x 10¹⁶ W/m²

8 x 10⁸ W/m²

4 x 10⁹ W/m²

8 x 10⁵ W/m²

4 x 10¹⁷ W/m²

4 x 10¹⁵ W/m²

2 x 10⁴ W/m²