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.
27 exam-style questions on OCR GCSE Physics Beyond Earth. Each one has a worked solution and a mark scheme showing where the marks go.