$A$ charge $+Q$ is moving upwards vertically. It enters a magnetic field directed to the north. The force on the charge will be towards

The population $p(t)$ at time $t$ of a certain mouse species follows the differential equation $\frac{d p(t)}{d t}=0.5 p(t)-450$. If $p(0)=850$, then the time at which the population becomes zero is

How many stereoisomers are possible for the following molecule?

The base current in a transistor circuit changes from $45 \mu A$ to $140 \mu A$. Accordingly,the collector current changes from $0.2 \text{ mA}$ to $4.0 \text{ mA}$. The current gain is

$A$ long straight rod of diameter $4 \ mm$ carries a steady current '$i$'. The current is uniformly distributed across its cross-section. The ratio of the magnetic fields at distances $1 \ mm$ and $4 \ mm$ from the axis of the rod is

The number of solutions $(x, y, z)$ to the system of equations $x+2y+4z=9$,$4yz+2xz+xy=13$,$xyz=3$,such that at least two of $x, y, z$ are integers is