A round steel plate with a diameter of 20 cm is supplied with heat in such a way that its temperature changes from 22 ° C to 150 ° C. How much does its area increase?

1.05×10⁻⁴ m²

Explanation:

ΔA = 2 A₀ α ΔT,

where ΔA is the change in area,

A₀ is the initial area,

α is the linear expansion coefficient,

and ΔT is the change in temperature.

A₀ = π (0.20 m / 2)² = 0.0314 m².

For steel, α = 13×10⁻⁶ /°C.

ΔT = 150°C − 22°C = 128°C.

ΔA = 2 (0.0314 m²) (13×10⁻⁶ /°C) (128°C)

ΔA = 1.05×10⁻⁴ m²

answer: option c. i.e. electric current flowing “downhill” from the negative electrode to the positive electrode in a battery

explanation:

the water analogy to the circuits define the pipes (water flows) to the electric current. now, we know that the electric current flows from the positive terminal to the circuit (as shown in the diagram attached).

hence, option c is the correct answer.

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.