Missing part in the text of the problem:
"<span>Water is exposed to infrared radiation of wavelength 3.0×10^−6 m"</span>
First we can calculate the amount of energy needed to raise the temperature of the water, which is given by

where
m=1.8 g is the mass of the water

is the specific heat capacity of the water

is the increase in temperature.
Substituting the data, we find

We know that each photon carries an energy of

where h is the Planck constant and f the frequency of the photon. Using the wavelength, we can find the photon frequency:

So, the energy of a single photon of this frequency is

and the number of photons needed is the total energy needed divided by the energy of a single photon:
The emerging velocity of the bullet is <u>71 m/s.</u>
The bullet of mass <em>m</em> moving with a velocity <em>u</em> has kinetic energy. When it pierces the block of wood, the block exerts a force of friction on the bullet. As the bullet passes through the block, work is done against the resistive forces exerted on the bullet by the block. This results in the reduction of the bullet's kinetic energy. The bullet has a speed <em>v</em> when it emerges from the block.
If the block exerts a resistive force <em>F</em> on the bullet and the thickness of the block is <em>x</em> then, the work done by the resistive force is given by,

This is equal to the change in the bullet's kinetic energy.

If the thickness of the block is reduced by one-half, the bullet emerges out with a velocity v<em>₁.</em>
Assuming the same resistive forces to act on the bullet,

Divide equation (2) by equation (1) and simplify for v<em>₁.</em>

Thus the speed of the bullet is 71 m/s
<span>In Thomson experiment, why was the glowing beam repelled by a negatively charged plate, because the glowing beam was negatively charged. The glowing beam particles were attracted to the positive plate.
</span><span>J.JThomson proved that the cathode rays produced a stream of negatively charged particles called electrons. </span>
<h2>Given :</h2>
- total charge = 9.0 mC = 0.009 C
Each electron has a charge of :

For producing 1 Cuolomb charge we need :
Now, for producing 0.009 C of charge, the number of electrons required is :
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So, Number of electrons passing through the cross section in 3.6 seconds is :

Number of electrons passing through it in 1 Second is :
Now, in 10 seconds the number of electrons passing through it is :
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