Physics Test-4...

Two magnets, each of magnetic moment \(M\), are placed to form a cross at right angles to each other. The magnetic moment of the system will be:

The energy flux of sunlight reaching the surface of the earth is \(1.388 \times 10^{3} \mathrm{~W} \mathrm{m}^{-2}\). The number of photons (nearly) per square meter are incident on the earth per second is (Assume that the photons in the sunlight have an average wavelength of \(550 \mathrm{~nm}\) ).

The bob of a pendulum is released from a horizontal position \(A\) as shown in the figure. If the length of the pendulum is \(1.5\) m, what is the speed with which the bob arrives at the lowermost point \(B\), given that it dissipated \(5 \%\) of its initial energy against air resistance?

In the circuit shown in diagram, \(R=\sqrt{\frac{L}{C}}\). Switch \(S\) is closed at time \(t=0\). The current through \(C\) and \(L\) would be equal after a time \(t\), equal to:

Two masses A and B of \(10\) kg and \(5\) kg respectively are connected with a string passing over a frictionless pulley fixed at the corner of a table as in figure. The coefficient of friction of A with the table is \(0.2\). The minimum mass of C that may be placed on A to prevent it from moving is equal to:

An electric dipole of length \(2\) cm is placed with its axis making an angle of \(30°\)to a uniform electric field \(10^5\) N/C. If it experiences a torque of \(10\sqrt{3}\) Nm, then potential energy of dipole -

A lens has focal length \(+20 \mathrm{cm}\). Its power will be:

In the circuit shown in diagram switch \(S\) is closed at time \(t = 0\). The charge which passes through the battery in one time constant is:

A horizontal platform with an object placed on it is executing SHM in the vertical direction. The amplitude of oscillation is \(2.5 \mathrm{~cm} .\) What must be the least period of these oscillations so that the object is not detached from the platform.

Calculate the ratio of \(rms\) speeds of oxygen gas molecules to that of hydrogen gas molecules kept at the same temperature.

A common emitter amplifier has a voltagegain of 50, an input impedance of \(100 \Omega\) and an output impedance of \(200 \Omega\). The power gain of the amplifier is:

A copper wire \(2 \mathrm{~m}\) long is stretched by \(1 \mathrm{~mm}\). If the energy stored in the stretched wire is converted to heat, calculate the rise in temperature of the wire. (Given, \(Y=12 \times 10^{11}\) dyne \(\mathrm{cm}^{-2}\), density of copper \(=9~\mathrm{gcm}^{-3}\) and specific heat of copper \(=0.1\) \(cal\) \(\left.\mathrm{g}^{-1 \circ} \mathrm{C}^{-1}\right)\)

If the shear modulus of a wire material is \(5.9 \times 10^{11}\) dyne \(\mathrm{cm}^{-2}\) then the potential energy of a wire of \(4 \times 10^{3} \mathrm{~cm}\) in diameter and \(5 \mathrm{~cm}\) long twisted through an angle of \(10^{\circ}\), is:

For the given uniform square lamina \(\mathrm{ABCD}\), whose centre is \(\mathrm{O}\).

Two vectors both are equal in magnitude and have their resultant equal in magnitude of the either. Find the angle between the two vectors.