A television picture is built up by scanning successive horizontal lines across the screen. It takes about 50 microseconds to scan the screen width. Ghosting refers to a weak horizontally displaced re

Question

A television picture is built up by scanning successive horizontal lines across the screen. It takes about 50 microseconds to scan the screen width. Ghosting refers to a weak horizontally displaced repetition of the main picture. These occur when the TV displays an additional delayed signal, due to reflection from an object such as a hill. If the ghost picture is displaced by 10% of the screen width, what is the additional path length of the reflected signal?

TestHub · Accepted Answer

Ghost displacement is 10% of the screen width, so the extra delay is $Delay = 0.1 \times 50 μ s = 5 μ s$ .

The reflected signal covers this extra path at speed c: $Extra path = 3 \times 1 0^{8} \times 5 \times 1 0^{- 6} = 1500 m = 1.50 km$ .

Option (B).

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