Equilibrium occurs when : answers:
the net force on the object is zero.
all the forces acting on an object are balanced.
the sum of the +x forces on an object equals the sum of the âx forces.
the sum of the upward forces equals the sum of the downward forces.

All are correct.

Explanation:

The equilibrium of an object occurs when:

1. The net force on the object is zero: When the number of forces acting on an object and the sum of all the forces is zero, then we say that the net force acting on the object is zero. It means that the net acceleration of the object is zero, it means the object is at rest or moving with constant velocity.

2. All forces acting on an object are balanced: When a number of forces acting on the object and the net force is zero it means all the forces are balanced. So, that the object has either zero velocity or moving with constant velocity.

3. The sum of +X forces on an object equals the sum of the - x forces: As the forces in + X axis direction is equal to the forces in - X axis direction, it means again the net force on the object is zero.

4. The sum of upward forces equal to the sum of downward forces: As the sum of forces in upwards direction is equal to the sum of forces in downward direction, it means the net force on the object is zero..

the higher the current the higher the mag field around it the higher the influence on the compass

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.