A vernier callipers has 20 divisions on the vernier scale, which coincides with $$1^{\text {th }}$$ division on the main scale. The least count of the instrument is $$0.1 \mathrm{~mm}$$. One main scale division is equal to ________ mm.

Time periods of oscillation of the same simple pendulum measured using four different measuring clocks were recorded as $$4.62 \mathrm{~s}, 4.632 \mathrm{~s}, 4.6 \mathrm{~s}$$ and $$4.64 \mathrm{~s}$$. The arithmetic mean of these readings in correct significant figure is :

Applying the principle of homogeneity of dimensions, determine which one is correct, where $$T$$ is time period, $$G$$ is gravitational constant, $$M$$ is mass, $$r$$ is radius of orbit.

The equation of stationary wave is :

$$y=2 \mathrm{a} \sin \left(\frac{2 \pi \mathrm{nt}}{\lambda}\right) \cos \left(\frac{2 \pi x}{\lambda}\right) \text {. }$$

Which of the following is NOT correct :