How many nodal tissues (specialized cardiac musculature) are present in the human heart?

An air bubble of radius $1 \ cm$ rises from the bottom portion through a liquid of density $1.5 \ g/cc$ at a constant speed of $0.25 \ cm/s$. If the density of air is neglected,the coefficient of viscosity of the liquid is approximately,(in $Pa \cdot s$):

The equation $\sqrt{3} \sin x + \cos x = 4$ has

In a mass spectrometer used for measuring the masses of ions,the ions are initially accelerated by an electric potential $V$ and then made to describe semicircular paths of radius $R$ using a magnetic field $B$. If $V$ and $B$ are kept constant,the ratio $\left( \frac{\text{charge on the ion}}{\text{mass of the ion}} \right)$ will be proportional to

Two identical rods of copper and iron are coated with wax uniformly. When one end of each is kept at the temperature of boiling water,the lengths up to which wax melts are $8.4 \ cm$ and $4.2 \ cm$,respectively. If the thermal conductivity of copper is $0.92$,then the thermal conductivity of iron is:

$A$ plane is parallel to two lines whose direction ratios are $1, 0, -1$ and $-1, 1, 0$ and it contains the point $(1, 1, 1)$. If it cuts the coordinate axes at $A, B, C$,then the volume of the tetrahedron $OABC$ (in cubic units) is