A ray of light travelling in air is incident on one face of a parallel glass slab of thickness $t$ and refractive index $\mu$ at an angle of incidence $i$ .Total time spent by the ray inside the slab is
$\frac{\mu^2 t}{c \sqrt{1-\mu^2 \sin i}}$
$\frac{\mu t}{c \sqrt{\mu^2-\sin ^2 i}}$
$\frac{\mu^2 t}{c \sqrt{\mu^2-\sin ^2 i}}$
$\frac{t}{c \sqrt{\mu^2-\sin ^2 i}}$
Radiation of wavelength $\lambda$ is incident on a photocell.The fastest emitted electron has speed $v$ . If the wavelength is changed to $\frac{3 \lambda}{4}$ ,then the speed of the fastest emitted electron will be
greater than $v \sqrt{\frac{4}{3}}$
less than $v \sqrt{\frac{4}{3}}$
equal to $v \sqrt{\frac{4}{3}}$
equal to $v \sqrt{\frac{3}{4}}$
Two spherical soap bubbles of radii $r_1$ and $r_2$ in vaccum coalesce under isothermal condition.The newly formed bubble has a radius( $r$ )given by
$r_1+r_2$
$\frac{r_1+r_2}{2}$
$\frac{r_1 r_2}{r_1+r_2}$
$\sqrt{r_1^2+r_2^2}$
A radioactive element ${ }_{92}^{242} \mathrm{X}$ emits two $\alpha$-particles,one electron and two positrons.The transformed nucleus is represented by ${ }_P^{234} Y$ .The value of $P$ is
85
87
92
96
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