Physics

1.2 We all know that light travels in a straight line. When Huygens established his wave theory, it was a 'heresy'. Afterwards, it became a 'dogma' as reflection, refraction etc. could be successfully explained on the basis of wave theory.

Initially it was believed that light was only energy but when photoelectric effect was discovered, it was proposed that light had a particle nature also. This was treated as 'heresy'. Later on Einstein proved it by his quantum theory of light and it became a 'dogma'.

1.1 The world is full of surprises. There are so many things happening with everyone, sometimes it becomes difficult to comprehend by us. But all the things can be explained by basic laws of sciences. Thus the incomprehensible things around us become comprehensible when we look at from scientific viewpoint.

2.3 

1 Calorie = 4.2 J = 4.2 kgm²s^-2

Standard formula for conversion

Given unit / New unit = (M1/M2)^x (L1/L2)^y (T1/T2)^z

Formula for energy = M¹L²T^-2

Here x = 1, y = 2, z = -2

In this problem

M1 = 1 kg, L1 = 1 m, T1 = 1 s and

M2 =? kg, L2 =? m, T2 =? s

So 1 Calorie = 4.2 (1/? )¹ (1/? )² (1/? )^-2

= 4.2? ^-1? ^-2? ²

Ans.4.1 A scalar quantity depends only on the magnitude – volume, mass, speeds, density, number of moles, angular frequency are all scalar quantities.

A vector quantity depends on magnitude and direction – velocity, acceleration, displacement and angular velocity are all vector quantities.

The net magnetic flux through any closed surface is zero, according to Gauss's Law for magnetism.
Mathematically,
? B · dA = 0.
It states that all magnetic field lines that enter a surface must exit from it as well. In this way, it is different from the electric charges which can exist independently as positive and negative.

The Earth's magnetic field makes a magnetic inclination or dip with the horizontal plane at a particular location. It shows how much the magnetic field is tilted from the horizontal. It gets tilted due to the Earth's magnetic nature. The formula is:
tan I = B_V / B_H,
where B_V is the vertical component and B_H is the horizontal component of the Earth's magnetic field.