Photon Momentum Radiation Pressure Quiz: Test Your Insight

Grade 11th

Reviewed by Ekaterina Yukhnovich

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By Thames

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| Questions: 20 | Updated: Mar 13, 2026

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1. Momentum conservation works best when you include both matter and ______ contributions.

Concept: system momentum. In modern physics, radiation can carry significant momentum. Accounting for it ensures conservation laws remain valid.

Explanation

Concept: system momentum. In modern physics, radiation can carry significant momentum. Accounting for it ensures conservation laws remain valid.

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About This Quiz

Photon Momentum Radiation Pressure Quiz: Test Your Insight - Quiz

This assessment explores the principles of photon momentum and radiation pressure. It evaluates your understanding of how light exerts force and the underlying physics concepts. Engaging with this material enhances your grasp of advanced optics and is essential for students and professionals in physics or engineering fields.

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2. Grade 11 wrap-up (less obvious): the cleanest reason light must have momentum is that otherwise:

It would travel slower

Momentum conservation would fail in emission/absorption processes

Mirrors wouldn’t reflect

Energy wouldn’t exist

Concept: conservation requirement. If light carried no momentum, a recoiling source couldn’t balance momentum. Experiments show recoil and pressure, confirming momentum carriage.

Explanation

Concept: conservation requirement. If light carried no momentum, a recoiling source couldn’t balance momentum. Experiments show recoil and pressure, confirming momentum carriage.

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3. It is possible for a system to lose energy by emitting light while keeping total momentum zero if emission is symmetric.

True

False

Concept: energy vs momentum balance. Energy and momentum are linked but not identical. Symmetric emission can cancel momentum while still carrying away energy.

Explanation

Concept: energy vs momentum balance. Energy and momentum are linked but not identical. Symmetric emission can cancel momentum while still carrying away energy.

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4. Which statement is the best 'big picture' idea?

Momentum is only mv

Momentum is a conserved quantity that must be defined correctly for high-speed motion and for light

Momentum is optional

Momentum depends on colour

Concept: correct definitions matter. In SR, momentum includes γ and applies to radiation. This keeps conservation laws universal.

Explanation

Concept: correct definitions matter. In SR, momentum includes γ and applies to radiation. This keeps conservation laws universal.

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5. If a system emits light symmetrically in opposite directions, the net momentum carried away is:

Large to the right

Large to the left

Approximately zero

Negative infinity

Concept: momentum cancellation. Equal opposite photon momenta cancel. The system can lose energy without changing net momentum.

Explanation

Concept: momentum cancellation. Equal opposite photon momenta cancel. The system can lose energy without changing net momentum.

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6. Photon momentum can be important in very precise measurements (like interferometers).

True

False

Concept: precision effects. Light can exert tiny forces that matter in sensitive setups. In some experiments, this must be considered.

Explanation

Concept: precision effects. Light can exert tiny forces that matter in sensitive setups. In some experiments, this must be considered.

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7. Which statements are correct?

Photons carry momentum

Radiation pressure is a result of momentum transfer

Reflection causes a larger momentum change than absorption

Photons have negative rest mass

Concept: photon facts. Photons have zero rest mass, not negative. The other statements are standard consequences of photon momentum.

Explanation

Concept: photon facts. Photons have zero rest mass, not negative. The other statements are standard consequences of photon momentum.

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8. Which of the following is a reason SR revises momentum?

To match weather patterns

To keep conservation laws consistent when c is invariant

To remove units from physics

To make gravity weaker

Concept: invariance of c. SR demands c is the same in all inertial frames. That requirement changes how momentum and energy must behave.

Explanation

Concept: invariance of c. SR demands c is the same in all inertial frames. That requirement changes how momentum and energy must behave.

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9. If a mirror reflects a beam, the beam’s momentum changes direction, increasing the momentum change compared with absorption.

True

False

Concept: impulse and force. Force relates to rate of change of momentum. Reflection roughly doubles the change compared to absorption for the same incoming beam.

Explanation

Concept: impulse and force. Force relates to rate of change of momentum. Reflection roughly doubles the change compared to absorption for the same incoming beam.

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10. Which statement is most accurate?

Light cannot push anything

Light can push because it transfers momentum when absorbed or reflected

Light pushes only in water

Light pushes because it has weight on earth

Concept: momentum transfer. The push comes from momentum exchange, not from 'weight.' It works even in vacuum.

Explanation

Concept: momentum transfer. The push comes from momentum exchange, not from 'weight.' It works even in vacuum.

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11. A photon has:

Rest mass and no momentum

No rest mass but it does have momentum

No energy

Negative momentum always

Concept: photon momentum. Photons carry energy and momentum even without rest mass. This is why light can push on surfaces.

Explanation

Concept: photon momentum. Photons carry energy and momentum even without rest mass. This is why light can push on surfaces.

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12. A practical example where photon momentum matters is:

Cooking pasta

Solar sails

Measuring room humidity

Paper folding

Concept: radiation pressure in practice. Solar sails use light pressure from the sun to generate thrust. This is small but can act continuously.

Explanation

Concept: radiation pressure in practice. Solar sails use light pressure from the sun to generate thrust. This is small but can act continuously.

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13. “Relativistic momentum” is only for objects very close to c; it never matters for light.

True

False

Concept: light is intrinsically relativistic. Light always travels at c, so relativistic treatment is essential. Photon momentum is a standard relativistic concept.

Explanation

Concept: light is intrinsically relativistic. Light always travels at c, so relativistic treatment is essential. Photon momentum is a standard relativistic concept.

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14. Why is photon momentum important in lasers and optics?

It changes chemical reactions

It can exert force (optical tweezers, radiation pressure effects)

It makes c variable

It cancels gravity

Concept: applications. Light forces can trap or move tiny particles. These effects rely on momentum transfer from photons.

Explanation

Concept: applications. Light forces can trap or move tiny particles. These effects rely on momentum transfer from photons.

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15. A box emits a photon to the right. What happens to the box (in the simplest isolated picture)?

It stays perfectly still

It recoils slightly to the left

It accelerates to the right

It loses all mass instantly

Concept: recoil and conservation. Total momentum must remain conserved. If the photon carries momentum rightward, the box must gain equal leftward momentum.

Explanation

Concept: recoil and conservation. Total momentum must remain conserved. If the photon carries momentum rightward, the box must gain equal leftward momentum.

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16. In an isolated system, photon momentum must be included to conserve total momentum.

True

False

Concept: complete accounting. If a system emits light, the light carries momentum away. Ignoring it would break momentum conservation in the calculation.

Explanation

Concept: complete accounting. If a system emits light, the light carries momentum away. Ignoring it would break momentum conservation in the calculation.

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17. Which is a correct qualitative statement?

Only massive objects have momentum

Any object or radiation with energy can carry momentum

Momentum exists only in air

Momentum is the same as temperature

Concept: momentum as motion/transport. Momentum is not restricted to massive objects. Light and other radiation transport momentum.

Explanation

Concept: momentum as motion/transport. Momentum is not restricted to massive objects. Light and other radiation transport momentum.

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18. In relativity, energy and momentum are linked; light carries both energy and ______.

Concept: energy–momentum link. Even without rest mass, light has energy and momentum. This is central in modern physics and technology.

Explanation

Concept: energy–momentum link. Even without rest mass, light has energy and momentum. This is central in modern physics and technology.

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19. Which interaction transfers more momentum to a surface (same light intensity)?

Absorption only

Reflection (bounces back)

Transmission only

No interaction transfers momentum

Concept: momentum change. Reflection reverses the photon’s direction, giving a larger change in momentum. A larger momentum change implies a larger force.

Explanation

Concept: momentum change. Reflection reverses the photon’s direction, giving a larger change in momentum. A larger momentum change implies a larger force.

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