Two metal spheres, one of radus \(R\) and the other of radius \(2 R\) respectively have the same surface charge density \(\sigma\). They are brought in contact and separated. What will be the new surface charge densities on them?

A person standing on the floor of an elevator drops a coin. The coin reaches the floor in time \(t_{1}\) if the elevator is at rest and in time \(t_{2}\) if the elevator is moving uniformly. Then

Given below are two statements: one is labelled as Assertion \(A\) and the other is labelled as Reason \(R\). Assertion \(A\): The potential ( \(V\) ) at any axial point, at \(2 \mathrm{~m}\) distance ( \(r\) ) from the centre of the dipole of dipole moment vector \(\vec{P}\) of magnitude, \(4 \times 10^{-6} \mathrm{C} \mathrm{m}\), is \(\pm 9 \times 10^3 \mathrm{~V}\). (Take \(\frac{1}{4 \pi \epsilon_0}=9 \times 10^9 \mathrm{Sl}\) units) Reason \(R\): \(V= \pm \frac{2 P}{4 \pi \epsilon_0 r^2}\), where \(r\) is the distance of any axial point, situated at \(2 \mathrm{~m}\) from the centre of the dipole. In the light of the above statements, choose the correct answer from the options given below:

\(\alpha\) -particle consists of 

A disc of radius \(2\; \mathrm{m}\) and mass \(100\; \mathrm{kg}\) rolls on a horizontal floor. Its centre of mass has speed of \(20\; \mathrm{cm} / \mathrm{s} .\) How much work is needed to stop it?

An oxygen cylinder of volume 30 litre has 18.20 moles of oxygen. After some oxygen is withdrawn from the cylinder, its gauge pressure drops to 11 atmospheric pressure at temperature \(27^{\circ} C\). The mass of the oxygen withdrawn from the cylinder is nearly equal to:
[Given, \(R=\frac{100}{12} J mol ^{-1} K^{-1}\), and molecular mass of \(O_2=32,1\) atm pressure \(=1.01 \times 10^5 N / m\)]

\(10\) resistors, each of resistance \(R\) are connected in series to a battery of \(emf\) \(E\) and negligible internal resistance. Then those are connected in parallel to the same battery, the current is increased \(n\) times. The value of \(n\) is :

A wire of resistance R is cut into 8 equal pieces. From these pieces two equivalent resistances are made by adding four of these together in parallel. Then these two sets are added in series. The net effective resistance of the combination is :

If \(c\) is the velocity of light in free space, the correct statements about photon among the following are: \(A\). The energy of a photon is \(E=h v\). \(B\). The velocity of a photon is \(c\). \(C\). The momentum of a photon, \(p=\frac{h v}{c}\). \(D\). In a photon-electron collision, both total energy and total momentum are conserved. \(E\). Photon possesses positive charge. Choose the correct answer from the options given below:

Which of the following oxoacids of phosphorus has strongest reducing property?

Which of the following represents the action of insulin ?

Match the Column \(- I\) with Column \(-II\)

Column \(-I\)	Column \(-II\)
\((a)\; P-\)wave	\((i)\) Depolarisation of ventricles
\((b)\; QRS\) complex	\((ii)\) Repolarisation of ventricles
\((c)\; T-\)wave	\((iii)\) Coronary ischemia
\((d)\) Reduction in the size of \(T-\)wave	\((iv)\) Depolarisation of atria
	\((v)\) Repolarisation of atria

Select the correct option \((a)\quad (b)\quad  (c) \quad (d)\)

In angiosperms, microsporogenesis and mega­ sporogenesis