1987 年

The wavelength and velocity of a sound in air are $25$ cm and $340\ \mathrm{m\,s^{-1}}$ respectively. When this sound enters a medium, its wavelength becomes $75$ cm. Find the velocity of the sound in the medium.

Which of the following has the shortest wavelength ?

A ray of light passes from air into a glass block. Which of the following ray diagrams is/are correct ? (Given that the critical angle of glass is $42^\circ$.)

An object is placed in front of a convex lens $L$ in the region $D'C'$, as shown in the diagram. If $F$ is the focus of the lens, where should the image lie ?

A concave lens is placed above the letter "d" which has the size shown in the above figure. The image of the letter "d" appears as

Which of the following ray diagrams is/are correct ?

Which of the following pairs of objects have different specific heat capacities ?

Arrange the following in ascending order. $E_1=$ Energy required to melt $1$ kg of ice at $0^\circ\mathrm{C}$ $E_2=$ Energy required to raise the temperature of $1$ kg of copper by $1^\circ\mathrm{C}$ $E_3=$ Energy required to vaporize $1$ kg of water at $100^\circ\mathrm{C}$ $E_4=$ Energy required to raise the temperature of $1$ kg of water by $1^\circ\mathrm{C}$

In the three-pin plug as shown, $X$, $Y$ and $Z$ are respectively connected to the

Four identical lamps $P$, $Q$, $R$ and $S$ are connected to a battery as shown above. If lamp $P$ is blown, which of the following would happen ?