Fundamental laws of physics require
- (a)conservation of energy and non-conservation of charge.
- (b)conservation of charge and non-conservation of linear momentum.
- (c)conservation of charge and non-conservation of energy.
- (d)conservation of energy, momentum and charge.
Correct — D, conservation of energy, momentum and charge. The great conservation laws of physics hold together: in an isolated system the total energy is conserved, the total linear momentum is conserved, and the total electric charge is conserved. No experiment has ever shown any of these three being created or destroyed, which is why the option that keeps all three is the only fully correct statement. Every other option denies at least one of them.
- (a)conservation of energy and non-conservation of charge. — Electric charge is strictly conserved and is never created or destroyed, so labelling charge as non-conserved is wrong.
- (b)conservation of charge and non-conservation of linear momentum. — Linear momentum of an isolated system is conserved, which is the basis of recoil and collisions, so calling it non-conserved is incorrect.
- (c)conservation of charge and non-conservation of energy. — Energy is conserved and only changes form, so denying its conservation contradicts the first law of thermodynamics.
Conservation laws state that certain physical quantities of an isolated system stay constant with time. The most fundamental are the conservation of energy, of linear momentum, and of electric charge, each supported by all experiments to date.
Each wrong option pairs one genuine conservation law with a false claim of non-conservation. Recognising that energy, momentum and charge are all conserved in an isolated system rules those out and leaves the all-inclusive option.
- The total energy of an isolated system is conserved; it changes form but is neither created nor destroyed.
- The total linear momentum of an isolated system is conserved when no external force acts.
- The total electric charge is conserved in every physical and chemical process.
- These conservation laws are among the most fundamental and thoroughly tested rules in physics.
All three, energy, momentum and charge, are conserved, so the all-inclusive option is correct.
- Thinking energy can be used up when it only changes form.
- Assuming momentum is not conserved when objects collide; it is, for the system as a whole.
Asked to choose the option that respects all the basic conservation laws; energy, momentum and charge are all conserved.
No directly related past PYQ was found.
- practice — not a real PYQ
When a gun recoils on firing a bullet, which quantity is conserved for the gun-and-bullet system?
- (a)energy only
- (b)linear momentum
- (c)charge only
- (d)none
Answer(b) linear momentum — the total stays zero, so the gun recoils.
- practice — not a real PYQ
The law of conservation of energy states that energy can be
- (a)created but not destroyed
- (b)destroyed but not created
- (c)neither created nor destroyed, only transformed
- (d)both created and destroyed
Answer(c) neither created nor destroyed, only transformed.