State the equivalence principle.

The diagram shows two identical boxes in two different states of motion.

In diagram 1 the box is in free fall close to the surface of a planet. In diagram 2 the box is accelerating in a region of space far from other masses.

A ray of monochromatic light is emitted from the base B of each box and is received at the top T of each box.

Observers at B measure the frequency of the emitted light to be ƒ₀.

State and explain, for each state of motion in diagram 1 and 2, if the frequency of light measured by an observer at T will be less than, equal to or greater than ƒ₀.

Radio signals, sent at the same time from Earth, reflect off two satellites X and Y as shown. The satellites are at the same distance from Earth.

The signal from Earth to satellite X and the reflected signal pass close to the Sun.

Compare, using the theory of general relativity, the arrival times at Earth of the signal from X and the signal from Y.

inertial/acceleration effects are indistinguishable from gravitational effects / a freely falling frame of reference in a gravitational field is equivalent to an inertial frame of reference / an accelerating frame of reference in outer space is equivalent to a frame of reference at rest in a gravitational field;

1: ƒ=ƒ_0;
because the frame of reference is equivalent to an inertial frame of reference;

2: ƒ<ƒ_0;
the frame of reference is equivalent to a frame of reference at rest in a gravitational field and so light is gravitationally red-shifted;

or

ƒ<ƒ_0;
observer at T will observe the source as though it was moving away from him and so will measure a Doppler red-shifted frequency;

the signal from satellite X will arrive after that from satellite Y / there will be a time delay in the arrival of signal X;
because the X signal undergoes gravitational time dilation/bends/curves (in the field of the Sun);