Gravitational Field Intensity due to Ring | JEE, NEET & CBSE Board Class 11 Exams Notes

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Gravitational Field Intensity due to Ring at point on the axis

Let us consider a ring of mass M, having radius ‘a’; the gravitational field at a distance x along its axis is found as follows:

Gravitational field intensity due to ring

Consider a small length element along the circumferential length of the ring which has a mass ‘dm’; the field intensity due to this length element is given by,

dE = G(dm/r2)

The vertical components of the fields cancel each other due to the symmetry of the ring, and only horizontal components survive and add up to,

\(\begin{array}{l}E = \int_{0}^{2\pi}\frac{Gdm}{r^{2}}cos\alpha\end{array} \)

Since

\(\begin{array}{l}cos\alpha =\frac{x}{\sqrt{{{x}^{2}}+{{a}^{2}}}}\end{array} \),

On substituting, we get

\(\begin{array}{l}E=\frac{GMx}{{{\left( {{x}^{2}}+{{a}^{2}} \right)}^{{}^{3}/{}_{2}}}}\end{array} \)

Which is the formula for Gravitational Field Intensity Due to a Ring at a distance x from center of ring of radius a.

**Note : At Center of ring, x = 0, so E = 0. Hence Gravitational Field Intensity at center of a Ring is zero.


Important Question-Answers on Gravitational Field Intensity Due to a Ring

Q1: What is the Gravitational Field Intensity?

A: The gravitational field intensity at a point is the force experienced by a unit mass placed at that point in the gravitational field of a body.

Q2: What is the Formula for Gravitational Field Intensity Due to a Ring?

A: The gravitational field intensity EE at a point P on the axis of a ring of mass MM and radius RR, at a distance xx from the center, is given by:

\(\begin{array}{l}E=\frac{GMx}{{{\left( {{x}^{2}}+{{a}^{2}} \right)}^{{}^{3}/{}_{2}}}}\end{array} \)

where:

  • G is the universal gravitational constant,
  • M is the mass of the ring,
  • R is the radius of the ring,
  • x is the distance of the point P from the center along the axis.

Q3: Why is the Gravitational Field at the Center of the Ring Zero?

A: At the center of the ring, the gravitational field due to each infinitesimal mass element of the ring cancels out symmetrically, leading to a net field intensity of zero.

Q4: How Does the Gravitational Field Vary Along the Axis?

A:

  • At the center of the ring (x = 0), the field is zero.
  • As x increases, the field initially increases, reaches a maximum, and then decreases asymptotically at large distances.

Q5: How Can This Concept Be Applied in Physics?

A: The concept of the gravitational field due to a ring is useful in astrophysics, planetary science, and engineering applications, including:

  • Understanding the gravitational effects of planetary rings.
  • Designing stable orbits in space missions.
  • Theoretical studies of symmetrical mass distributions.

FAQs on Gravitational Field Intensity Due to a Ring

Q1: Is the Gravitational Field Due to a Ring Uniform?

A: No, the gravitational field varies depending on the location of the point along the axis and is not uniform.

Q2: What Happens to the Gravitational Field as x → ∞?

A: As the distance x increases, the field intensity decreases and approximates the field due to a point mass MM at large distances.

Q3: What is the Direction of the Gravitational Field at a Point on the Axis?

A: The gravitational field is directed towards the center of the ring along the axis.


MCQs on Gravitational Field Intensity Due to a Ring

Q1: The gravitational field intensity at the center of a uniform ring is:

A) Maximum
B) Zero
C) Equal to GM/R²
D) Infinite

Answer: B) Zero
Explanation: The field intensity at the center cancels due to symmetry.

Q2: The gravitational field intensity due to a ring along its axis is maximum at:

A) The center of the ring
B) Infinity
C) A certain distance from the center
D) On the ring itself

Answer: C) A certain distance from the center
Explanation: The field first increases, reaches a maximum, and then decreases with distance.

Q3: The formula for the gravitational field intensity due to a ring is derived using:

A) Newton’s laws of motion
B) Newton’s law of gravitation
C) Einstein’s relativity
D) Kepler’s laws

Answer: B) Newton’s law of gravitation
Explanation: The field intensity is derived based on the inverse-square law of gravitation.


Test Your Knowledge

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Gravitational Field Intensity Due to Ring Quiz

const questions = [ { q: “What is the gravitational field intensity at the center of a uniform ring?”, options: [“Zero”, “Maximum”, “Infinity”, “Equal to mass of ring”], answer: 0, explanation: “At the center of a uniform ring, gravitational forces cancel out, making the field intensity zero.” }, { q: “What is the formula for gravitational field intensity on the axis of a ring?”, options: [“Gm/x²”, “Gmz/(x² + r²)^(3/2)”, “Gm/r²”, “Gmz/(x² + r²)”], answer: 1, explanation: “The field intensity on the axis of a ring is given by Gmz/(x² + r²)^(3/2).” }, { q: “How does gravitational field intensity change as we move along the axis of the ring?”, options: [“Increases then decreases”, “Remains constant”, “Continuously increases”, “Continuously decreases”], answer: 0, explanation: “The field first increases, reaches a maximum, and then decreases along the axis.” }, { q: “Where is the maximum gravitational field intensity due to a ring located?”, options: [“At the center”, “At infinity”, “At a certain distance along the axis”, “Equally throughout the axis”], answer: 2, explanation: “The field is maximum at a certain point along the axis, not at the center or infinity.” }, { q: “What happens to gravitational field intensity when the distance from the ring increases?”, options: [“Increases”, “Decreases”, “Remains the same”, “Becomes infinity”], answer: 1, explanation: “As distance increases, the field intensity decreases following inverse square law patterns.” }, { q: “What is the gravitational field inside the ring along the plane of the ring?”, options: [“Zero”, “Maximum”, “Infinity”, “Same as at the axis”], answer: 0, explanation: “Inside the ring in its plane, the gravitational field intensity is zero due to symmetry.” }, { q: “How does mass of the ring affect the gravitational field intensity?”, options: [“It does not affect”, “Field intensity is directly proportional to mass”, “Field intensity is inversely proportional to mass”, “Field intensity depends only on distance”], answer: 1, explanation: “The field intensity is directly proportional to the mass of the ring.” }, { q: “What happens if the radius of the ring increases while keeping mass constant?”, options: [“Field intensity increases”, “Field intensity decreases”, “Field remains unchanged”, “Field becomes zero”], answer: 1, explanation: “Increasing the radius spreads the mass over a larger area, reducing field intensity.” }, { q: “What is the nature of gravitational field intensity due to a ring?”, options: [“Vector quantity”, “Scalar quantity”, “Neither vector nor scalar”, “Both vector and scalar”], answer: 0, explanation: “Gravitational field intensity is a vector quantity because it has both magnitude and direction.” }, { q: “How does gravitational field intensity change inside a solid ring?”, options: [“It remains constant”, “It increases”, “It decreases”, “It is always zero”], answer: 3, explanation: “Inside a uniform ring, the gravitational field intensity is always zero due to symmetry.” } ];function loadQuiz() { let quizContainer = document.getElementById(“quiz”); quizContainer.innerHTML = “”; questions.forEach((q, index) => { let questionHTML = `
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