An obstacle is moving towards the source with velocity $$v$$. The sound is reflected from the obstacle. If $$c$$ is the speed of sound and $$\lambda$$ is the wavelength, then the wavelength of the reflected wave $$\lambda_r$$ is
If the angle of dip at places $$A$$ and $$B$$ are $$30^{\circ}$$ and $$45^{\circ}$$ respectively, then the ratio of horizontal component of earth's magnetic field at $$A$$ to that at $$B$$ will be $$\left[\sin 45^{\circ}=\cos 45^{\circ}=\frac{1}{\sqrt{2}}, \sin \frac{\pi}{6}=\frac{1}{2}, \cos \frac{\pi}{6}=\frac{\sqrt{3}}{2}\right]$$
The ratio of energy required to raise a satellite of mass $$m$$ to a height $$h$$ above the earth's surface of that required to put it into the orbit at same height is [$$R=$$ radius of the earth]
A circular coil of radius $$R$$ is carrying a current $$I_1$$ in anti-clockwise sense. A long straight wire is carrying current $$I_2$$ in the negative direction of $$X$$-axis. Both are placed in the same plane and the distance between centre of coil and straight wire is $$d$$. The magnetic field at the centre of coil will be zero for the value of $$d$$ equal to