Light is an electromagnetic wave. Its speed in vacuum is given by the expression

Photoelectric emission is observed from a metallic surface for frequencies $v_1$ and $v_2$ of the incident light rays $(v_1 > v_2)$. If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of $1 : k$,then the threshold frequency of the metallic surface is

The position vectors of points $A, B, C$ and $D$ are $\vec A = 3\hat i + 4\hat j + 5\hat k, \vec B = 4\hat i + 5\hat j + 6\hat k, \vec C = 7\hat i + 9\hat j + 3\hat k$ and $\vec D = 4\hat i + 6\hat j$. Then the displacement vectors $\overrightarrow{AB}$ and $\overrightarrow{CD}$ are:

The reading of the ammeter in the circuit shown will be: (in $A$)

Let $P, Q, R$ and $S$ be the points on the plane with position vectors $-2 \hat{i}-\hat{j}$,$4 \hat{i}$,$3 \hat{i}+3 \hat{j}$ and $-3 \hat{i}+2 \hat{j}$ respectively. Then the quadrilateral $PQRS$ must be a

Modern farmers have been able to increase rice production by $50\%$ using which of the following?