Tag: idea of energy

Questions Related to idea of energy

A window whose area is $2m^2$ opens on street where the street noise result in an intensity level at the window of $60db$. How much acoustic power enters the window via sound waves ? Now, if an acoustic absorber is fitted at the window? 

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $8\mu W$

  2. $10\mu W$

  3. $4\mu W$

  4. $2\mu W$

Show answer
Correct Option: D
Explanation:

Intensity = 60 dB

60 = 10 log $(\frac{I}{I _{ref}})$

where $I _{ref}$ is the refrence intensity , general value of this is given by 

$I _{ref} = 10^{-12}\frac{watt}{m^2}$

$\frac{I}{10^{-12}}$ = anti log (6)

$I = 10^{-12}  \times{anti log(6)} = 10^{-12} \times{10^6} = 10^{-6}$

Power = I$\times$ area = $2 \times{10^{-6}}$ watt

The internal energy change when a system goes from state A to B is $40$ kJ/mole. If the system goes from A to B by a reversible path and returns to state A by an irreversible path what would be the net change in internal energy?

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. $40$ kJ

  2. $> 40$ kJ

  3. $< 40$ kJ

  4. Zero

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Correct Option: D
Explanation:
For a cyclic process the net change in the internal energy is zero because the change in internal energy doesnot depend on the path.

Which of the following can be negative 

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. Kinetic energy

  2. Potential energy

  3. Mechanical energy

  4. All of these

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Correct Option: B,C
Explanation:

Mechanical energy & potential energy can be negative.

$\therefore$ Option $B$ and $C$.

If the unit of force and length be each increased by four times, then the unit of energy is increased by

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. 16 times

  2. 8 times

  3. 2 times

  4. 4 times

Show answer
Correct Option: A
Explanation:

Unit of Energy = Unit of Force $\times$ Unit of length 
So if we increase unit of length and force, each by four times, then unit of energy will increase by sixteen times.