Shallow water runs faster than deep river water. Why?

The equation of continuity is
area of cross-section of flow of water × velocity of water = constant.
Hence  the velocity of water is inversely proportional to the the area of cross-section of water flowing.
When water runs deep then the area of cross section of the flowing water is more than when its shallow so the velocity is less for deep water.

WHAT IS SUBLIMATION ?

Sublimation is a process of transformation of state of matter where a solid changes directly into its gaseous state.
The molecules in some solids have very weak force of attraction. So the molecules by gaining very little heat from the surrounding can change into gaseous particles.

Does specific resistance/resistvity change on stretching a wire?

Specific resistance or resistivity is the resistance of a wire of unit length and unit area of cross-section.

It depends on two factors.
1. Nature of the substance.
2.  Temperature of the substance

It is not effected by
1. Length of the wire.
2. Area of cross-section of the wire.

So., when you stretch a  wire its RESISTIVITY remains constant.

Can a solenoid be used to find the direction of earth's magnetic field ( magnetic North and magnetic south)?

A solenoid is a cylindrical/helical coil whose length is more than its diameter. When we pass current through the solenoid , a magnetic field is set up in the space around the solenoid similar to that of a bar magnet.
There is ,in fact, a strong and uniform field in the core of the solenoid.At the two ends of the solenoid, poles are developed as in a bar magnet.
So the current carrying solenoid if freely can show the direction of the magnetic field of a magnet.The north end of the magnet shows the geographic north and South end shows south .

Why is high voltage preferred for long distance transmission of electric power?

The electric power is generated at 11,000V at a power station. It is then transformed to 1,32,000V using a step up transformer.
For a given electric power, when voltage increases, the electric current decreases as P=VI or I=P/V.
Hence , at high voltage low current is involved.
As current decreases, the power loss(I in the transmission lines decreases in the form of heat .
To reduce this loss, high voltage is preferred

Sun rises in the east. Why

The earth has two types of motion.
1.Revolution around the sun
2. The rotation about it's own axis.

The earth rotates about it's own axis from west to east, so sun appears to rise from east direction.

Sea Breeze...How is it formed?

theloveforphysics

Water has higher specific heat capacity* than that of land(sand) due to which water is heated at slower rate than the land. As the land is heated, the hot air above the land rises up  creating low pressure above the land. As the air above water is comparatively cooler than the air above the land , this air moves towards the land due to the pressure difference. This cool breeze blowing towards the land from sea is called sea breeze.

As heating is required for its formation,  sea breeze blows during day time.

* Specific heat capacity is the amount of heat required to raise the temperature of unit mass of a substance by 1 K or 1°C.

Why do cooking vessels have thick bases?

theloveforphysics

Cooking vessel is provided with thick base to increase the mass so that its heat capacity increases and the base can absorb more heat and impart it to the food so that food is cooked quickly and the base remains hot for longer period of time

theloveforphysics

Why do we beat carpet to remove dust particles

theloveforphysics

  Before beating the carpet , both dust particles and carpet are at rest. Hence the dust  particles have inertia of rest. When carpet is beaten, its comes to motion but due to inertia of rest, dust particles remains at rest and are separated.

Camels have broad feet. Why?

theloveforphysics

Camels have broad feet so that they can walk on sand. As the area of their feet is more, the pressure due to their weight on the sand is less. So they can walk easily without sinking their feet on the sand.

Flash of lightning is seen before the sound of thunder. Why

   Both sound and light energy are released at the same time. In air the speed of light is 300000000 m/s and speed of sound is 340 m/s. Hence the light reaches the observer instantly and sound after some time.

    For example, if an electric discharge  between the clouds takes place at a distance of 1km from the observer then lightning flash is seen instantly but sound of thunder will be heard after about 3 seconds.

Why is nuclear fusion difficult to start?

Nuclear fusion is the process of combination of lighter nuclei (eg. hydrogen)  to form a heavier nucleus. When two lighter nuclei come close to each other, there is strong electrostatic force of repulsion between the nuclei. So this process is difficult.

To carry out this process high temperature (=10000000 K ) and pressure is required. Hence it is also called thermo-nuclear reaction.

Freezer compartment of a refrigerator is placed at its top portion. Why?

Cold air from the freezing compartment settles down owing to its higher density and keeps the temperature of the contents below it low.

Infrared rays are used for thermal photography?

Infrared rays are invisible rays whose wavelength is more than that of red colour.They produce heating effect. As they have long wavelength, they are least scattered by the fog, mist and smog and dust particles. As they effect a specially treated photographic plate due to the heating effect, they are used in thermal photography.

THE DIFFERENCE BETWEEN AC AND DC.

                        ALTERNATING CURRENT
1. Its value changes continuously.
2. Its polarity changes periodically.
3. It can be transformed by a transformer.

                         DIRECT CURRENT

1. Its value doesn't change, it has  a constant magnitude.
2. Its polarity doesn't  change.
3. It can not be transformed by transformer.

The temperature is lower in shade than in direct sunlight, why ?

In the direct sunlight there are Infrared Rays. Infrared rays have strong heating effect. But in shade there is no direct sunlight with these heating Rays. Only reflected or diffused light is there. So, temperature is lower in  shade than in direct  sunlight

A spanner has long handle. Why?

A spanner is used to turn a nut to open or tighten it.
The rotational effect depends on the perpendicular distance between the force and the point of application of force. When we increase the perpendicular distance then the Moment of force increases keeping the moment same.

Efficiency of a machine is always less than 100%. Why?

Efficiency is the ratio of work output and work input. As work output is always less than work output for the following reasons, the efficiency is less than 1 or 100%.

1. The movable parts of a machines are not weightless.
2.  The movable parts are not frictionless.
3.  The parts of the machines are not rigid.
4. The strings or belts are not perfectly elastic in nature.

Why is electromagnet made of soft iron?

Electromagnet is a temporary magnet made of soft iron. Soft iron is magnetised by the magnetic field of a coil or solenoid.
Soft iron has high magnetic permeability due to which it gets magnetised quickly and it loses magnetic properties easily due to the fact that it has low magnetic retentivity .

Why are Liquids heated from below?

A liquid in a vessel is heated due to the process of convection. In convection heat is transferred by the actual movement of heated particles in upward direction. As the liquid is heated from below its density decreases and hence it rises up and cold liquid settles down and heated. This process continues till whole liquid is heated.

IF WE KEEP REFRIGERATOR DOOR OPEN, WILL IT ABLE TO KEEP THE ROOM COOL?

For a moment, it seems like that !
But the compressor does work to extract heat from the content and this heat is thrown out from the refrigerator.

If we keep the door open for long time then heat is taken from the room (from front portion)and thrown back to the room. So the temperature of the room remains the same. Hence, the refrigerator will not be able to keep the room cool.