It is possible to take a high quality photograph of a very fast moving object by illuminating the
Channel: Doubtnut
Date: 12/04/2020

It is possible to take a high quality photograph of a very fast moving object by illuminating the object for quite a small fraction of a second. You may have come across photographs of a bullet penetrating a banana or an apple in many text books or magazines. This is called 'stop action' photography because the fast moving object travels a very short distance during the time of illumination. Harold Edgerton, the inventor of stroboscope, was a pioneer of this kind of photography. A normal photographic plate works properly if it receives an energy of 4J during the exposure. To release this energy in a very small fraction of time, huge amount of power is required. Such huge power can not be generated directly from a battery because of its high internal resistance. To produce such power a capacitor is used. The time in which a capacitor discharges can be very short. Although, theoretically it would take a long time for a capacitor to discharge completely, it discharges almost completely in about 10 time constant. Consider the following situation A capacitor of 200muF storing 4J energy is made to discharge through a flash light in 2ms. This setup is used to take the picture of a bullet moving at a speed of `100m//s` Assume that the flash light acts as a resistor and there is no other resistance in the circuit.   If we use a lens of power 10 diopters, the lens to photographic plate distance is 15cm and the bullet moves perpendicular to the principal axis, what is the distance covered by bullet as seen on photographic plate.