A deep-space probe is on a direct return trajectory to Earth, accelerating under gravity towards a terrestrial tracking station. It continuously transmits a radio telemetry signal of constant emitted frequency femitf_{\text{emit}}femit and wavelength λemit\lambda_{\text{emit}}λemit.
As the probe accelerates towards the station, how do the observed frequency fobsf_{\text{obs}}fobs, the observed wavelength λobs\lambda_{\text{obs}}λobs, and the propagation speed of the radio waves vwavev_{\text{wave}}vwave detected by the station change over time?
fobs>femitf_{\text{obs}} > f_{\text{emit}}fobs>femit and is increasing; λobs<λemit\lambda_{\text{obs}} < \lambda_{\text{emit}}λobs<λemit and is decreasing; vwavev_{\text{wave}}vwave remains constant at ccc.
fobs>femitf_{\text{obs}} > f_{\text{emit}}fobs>femit and remains constant; λobs<λemit\lambda_{\text{obs}} < \lambda_{\text{emit}}λobs<λemit and remains constant; vwavev_{\text{wave}}vwave remains constant at ccc.
fobs>femitf_{\text{obs}} > f_{\text{emit}}fobs>femit and is increasing; λobs<λemit\lambda_{\text{obs}} < \lambda_{\text{emit}}λobs<λemit and is decreasing; vwavev_{\text{wave}}vwave is greater than ccc and is increasing.
fobs<femitf_{\text{obs}} < f_{\text{emit}}fobs<femit and is decreasing; λobs>λemit\lambda_{\text{obs}} > \lambda_{\text{emit}}λobs>λemit and is increasing; vwavev_{\text{wave}}vwave remains constant at ccc.
Practise OCR GCSE Physics Beyond Earth with exam-style questions for Foundation and Higher tier. 50 questions, matched to the OCR GCSE Physics (J249) specification and written in Paper 1 and Paper 2 (Foundation Tier) or Paper 3 and Paper 4 (Higher Tier) style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.