What is the answer, am confused

Which statement is true for light passing into a medium that is more optically dense than the first medium through which it past

Your target variable is δf, the magnitude of the difference in frequency between the waves emitted from the sonar device and the waves received by the device after reflecting off the whale. write an expression for δf in terms of the relevant frequencies using the subscript notation introduced above.

The discovery of the electron as a subatomic particle was a result of