A man stands in front f a high wall and produces a sound. If he receives the echo of the sound four seconds later, what is his distance from the wall? [The speed of sound in air is 330ms-1]
A negatively charged rod is brought near the cap of an electroscope. The cap is earthed momentarily while the charge is near to it. The rod is then removed. Which statement is correct?
A.
The cap will be positively charged and the leaf will be negatively charged
B.
The cap will be negatively charged and the leaf will be positively changed
C.
The cap and the leaf will be positively charged
D.
The cap and the leaf will be negatively charged
