An electric bulb, connected to a make and break power supply, switches off and on every second in its rest frame. What is the frequency of its switching off and on as seen from a spaceship travelling at a speed 0.8c?
As the Lorentz transformation suggests there will be time dilation for a moving object with respect to rest frame which is given by 
Where 
, V is velocity of moving object and C is speed of light in vacuum i.e. 
And 
is time in rest frame.
ATQ, . 
Time taken by the bulb to switch off and switch on with respect to spaceship will be 
Frequency will be 
1