Why is loud sound heard during the process of Resonance?

Loudness depends on the amplitude of sound wave . In resonance, amplitude increases when natural frequency matches with the frequency of external force. As amplitude increases, loudness of the sound increases.

FOCUS OF A CONCAVE MIRROR

Focus is a point on the principal axis where the incident rays parallel to the principal axis meet after reflection. Highly diminished image is formed at focus if the object is
placed at infinity.

When does a nucleus become unstable?

A nucleus becomes unstable when number of neutrons in the nucleus is  more than the number of protons

Why is handle fitted near the edge of a door?

The moment of force directly proportional to the force and perpendicular distance of force from the axis of rotation. For a given moment of force, smaller force is required if it is applied at a longer distace from the axis of rotation. To open the door with least force ,handle is fitted near its edge.

Principle of moments

Principle of MOMENTS states that in EQUILIBRIUM the sum of clockwise MOMENT is equal to the sum of anti clockwise MOMENT.

Why do we need moisturizers in winters?

Winters in most places have very low humidity. For that,  the moisture of our body is lost easily and skin becomes dry quickly.

Temperature of surrounding falls during or after the heavy shower. Why?

Temperature of any medium or object falls when it loses the heat. After the heavy shower, water absorbs heat from the surrounding air. Water has high specific heat capacity (i.e. the quantity of heat required by unit mass for the unit rise of temperature)  so water absorbs large amount heat from the surrounding without much rise in it's own temperature. Hence, temperature falls.

Why is food cooked faster in pressure cooker?

Water boils at 100°C at normal pressure of 1 arm or 100000 Pascal. Boiling temperature increases  with the increase in pressure above the liquid surface. When we cook food in pressure cooker, the pressure increases due the retention of vapour and hence the boiling temperature increases in the pressure cooker upto 125°C As food is cooked at higher temperature than 100°C , it is cooked faster in the pressure cooker.

SI UNIT OF TEMPERATURE

Why is Kelvin considered as SI unit of temperature?

Answer: From kinetic theory of matter , it is understood that the average kinetic energy of molecule is directly proportional to the  temperature in Kelvin. When the temperature in this scale is zero then the molecular motion ceases irrespective of nature of any substance. This can be taken as the starting temperature . Hence Kelvin scale is taken as an absolute scale and hence SI unit.

What is loudness of a sound?

Loudness of a sound is the characteristic of a sound which depend on the intensity of  energy it carries.
Intensity of a sound is the amount of energy passing through a surface area of one square metre held perpendicular per sec.
Intensity depends on square of amplitude of the wave passing. Hence we can say Loudness is directly proportional to the square of Amplitude. If amplitude is doubled, loudness becomes four times.
Loudness depends on distance of source from the listener.
Loudness depends on resonance also.

ARCHIMEDES' PRINCIPLE

"Any body immersed partially or completely in a fluid experiences an upthrust which is equal to the weight of the fluid displaced by the immersed part of the body"

Ideal fuel

What  are the characteristics of an ideal fuel?

Answer: The characteristics are:
 1. It has high calorific value. It means the fuel produces large amount of energy per unit mass  of fuel on burning .
 2. It should not emit harmful gases or products on burning.
 3.It should  easily be stored and transported .

Different persons have different voice. Why?

Each vibrating body has it's own set of frequencies. The minimum frequency of any vibrating body is called its fundamental note. Other frequencies are called harmonics. Combining these two types of frequencies , we get its waveform. The waveform decides the types ( Quality) of sound produced.

      As each source has it's own quality of sound, different sources or different persons have different type of sound.