. For a transistor, the current ratio ' $\beta_{d c}$ ' is defined as the ratio of

A clock pendulum having coefficient of linear expansion. $\alpha=9 \times 10^{-7} /{ }^{\circ} \mathrm{C}^{-1}$ has a period of 0.5 s at $20^{\circ} \mathrm{C}$. If the clock is used in a climate, where the temperature is $30^{\circ} \mathrm{C}$, how much time does the clock lose in each oscillation? ( $g=$ constant)

Two capillary tubes of different diameters are dipped in water. The rise of water is

A thin hollow prism of refracting angle $3^{\circ}$, filled with water gives a deviation of $1^{\circ}$. The refractive index of water is