JEE Mains · Physics · STD 12 - Electric charges and fields
- JEE Mains 2025
- Medium
- Numerical
A positive ion \(A\) and a negative ion \(B\) has charges \(6.67 \times 10^{-19} \mathrm{C}\) and \(9.6 \times 10^{-10} \mathrm{C}\), and masses \(19.2 \times 10^{-27} \mathrm{~kg}\) and \(9 \times 10^{-27} \mathrm{~kg}\) respectively. At an instant, the ions are separated by a certain distance r. At that instant the ratio of the magnitudes of electrostatic force to gravitational force is \(P \times 10^{45}\), where the value of 10\(P\) is _______.
(Take \(\frac{1}{4 \pi \varepsilon_0}=9 \times 10^9 \mathrm{Nm}^2 \mathrm{C}^{-1}\) and universal gravitational constant as \(6.67 \times 10^{-11} \mathrm{Nm}^2 \mathrm{~kg}^{-2}\) )
Assume that charge may not be an integral multiple of electrons.
Pick an option to check your answer.
Answer & Solution
Correct Answer
(A) 5
Step-by-step Solution
Detailed explanation
Explanation:
Let us calculate the ratio of forces step-by-step using Coulomb's Law and Newton's Law of Gravitation from the Physics curriculum, applying direct numerical cancellation:
Step 1: Write the formula for the ratio of forces
The electrostatic force (\(F_e\)) and gravitational force (\(F_g\)) between two sharing bodies separated by distance \(r\) are given by:
\(F_e = \frac{k \cdot |q_A| \cdot |q_B|}{r^2}\) and \(F_g = \frac{G \cdot m_A \cdot m_B}{r^2}\)
Taking the ratio eliminates the distance parameter (\(r^2\)) completely:
\(\frac{F_e}{F_g} = \frac{k \cdot |q_A| \cdot |q_B|}{G \cdot m_A \cdot m_B}\)
Step 2: Substitute the values and apply the smart cancellation trick
Substitute the given values into the equation:
\(\frac{F_e}{F_g} = \frac{(9 \times 10^9) \times (6.67 \times 10^{-19}) \times (9.6 \times 10^{-10})}{(6.67 \times 10^{-11}) \times (19.2 \times 10^{-27}) \times (9 \times 10^{-27})}\)
Separating the constant coefficients from the powers of 10:
\(\frac{F_e}{F_g} = \left[ \frac{9 \times 6.67 \times 9.6}{6.67 \times 19.2 \times 9} \right] \times \left[ \frac{10^9 \times 10^{-19} \times 10^{-10}}{10^{-11} \times 10^{-27} \times 10^{-27}} \right]\)
Now, cancel out the identical numbers directly without multiplying them:
- The \(9\) in the numerator cancels out with the \(9\) in the denominator.
- The \(6.67\) in the numerator cancels out with the \(6.67\) in the denominator.
- We are left with \(\frac{9.6}{19.2}\). Since \(19.2 = 2 \times 9.6\), this reduces beautifully to \(\frac{1}{2} = 0.5\).
Step 3: Simplify the powers of 10
- Numerator power = \(9 - 19 - 10 = -20\)
- Denominator power = \(-11 - 27 - 27 = -65\)
- Net power = \(-20 - (-65) = 45\)
Combining the components gives:
\(\frac{F_e}{F_g} = 0.5 \times 10^{45}\)
Step 4: Find the final value of \(10P\)
Comparing our result with the expression given in the question (\(P \times 10^{45}\)):
\(P = 0.5\)
Therefore:
\(10P = 10 \times 0.5 = 5\)
Hence, Option A is the correct choice.
Let us calculate the ratio of forces step-by-step using Coulomb's Law and Newton's Law of Gravitation from the Physics curriculum, applying direct numerical cancellation:
Step 1: Write the formula for the ratio of forces
The electrostatic force (\(F_e\)) and gravitational force (\(F_g\)) between two sharing bodies separated by distance \(r\) are given by:
\(F_e = \frac{k \cdot |q_A| \cdot |q_B|}{r^2}\) and \(F_g = \frac{G \cdot m_A \cdot m_B}{r^2}\)
Taking the ratio eliminates the distance parameter (\(r^2\)) completely:
\(\frac{F_e}{F_g} = \frac{k \cdot |q_A| \cdot |q_B|}{G \cdot m_A \cdot m_B}\)
Step 2: Substitute the values and apply the smart cancellation trick
Substitute the given values into the equation:
\(\frac{F_e}{F_g} = \frac{(9 \times 10^9) \times (6.67 \times 10^{-19}) \times (9.6 \times 10^{-10})}{(6.67 \times 10^{-11}) \times (19.2 \times 10^{-27}) \times (9 \times 10^{-27})}\)
Separating the constant coefficients from the powers of 10:
\(\frac{F_e}{F_g} = \left[ \frac{9 \times 6.67 \times 9.6}{6.67 \times 19.2 \times 9} \right] \times \left[ \frac{10^9 \times 10^{-19} \times 10^{-10}}{10^{-11} \times 10^{-27} \times 10^{-27}} \right]\)
Now, cancel out the identical numbers directly without multiplying them:
- The \(9\) in the numerator cancels out with the \(9\) in the denominator.
- The \(6.67\) in the numerator cancels out with the \(6.67\) in the denominator.
- We are left with \(\frac{9.6}{19.2}\). Since \(19.2 = 2 \times 9.6\), this reduces beautifully to \(\frac{1}{2} = 0.5\).
Step 3: Simplify the powers of 10
- Numerator power = \(9 - 19 - 10 = -20\)
- Denominator power = \(-11 - 27 - 27 = -65\)
- Net power = \(-20 - (-65) = 45\)
Combining the components gives:
\(\frac{F_e}{F_g} = 0.5 \times 10^{45}\)
Step 4: Find the final value of \(10P\)
Comparing our result with the expression given in the question (\(P \times 10^{45}\)):
\(P = 0.5\)
Therefore:
\(10P = 10 \times 0.5 = 5\)
Hence, Option A is the correct choice.
More questions from Physics
- In an experiment a convex lens of focal length \(15\, cm\) is placed coaxially on an optical bench in front of a convex mirror at a distance of \(5\,cm\) from it. It is found that an object and its image coincide, if the object is placed at a distance of \(20\,cm\) from the lens. The focal length of the convex mirror is.......\(cm\)JEE Mains 2017 Hard
- A square loop is carrying a steady current \(I\) and the magnitude of its magnetic dipole moment is \(m\). If this square loop is changed to a circular loop and it carries the same current, the magnitude of the magnetic dipole moment of circular loop will beJEE Mains 2019 Medium
- The mass of the moon is \(1 / 144\) times the mass of a planet and its diameter \(1 / 16\) times the diameter of a planet. If the escape velocity on the planet is \(\mathrm{v}\), the escape velocity on the moon will be _______.JEE Mains 2024 Hard
- A plane electromagnetic wave propagating in \(\mathrm{x}\)-direction is described by \(\mathrm{E}_{\mathrm{y}}=\left(200\ \mathrm{Vm}^{-1}\right) \sin \left[1.5 \times 10^7 \mathrm{t}-0.05\ \mathrm{x}\right] \text {; }\) The intensity of the wave is :(Use \(\epsilon_0=8.85 \times 10^{-12} \mathrm{C}^2 \mathrm{~N}^{-1} \mathrm{~m}^{-2}\) )JEE Mains 2024 Hard
- The minimum energy required by a hydrogen atom in ground state to emit radiation in Balmer series is nearly _______.JEE Mains 2024 Hard
- The temperature of an ideal gas is increased from \(200\,K\) to \(800\,K\). If r.m.s. speed of gas at \(200\,K\) is \(v_0\). Then, r.m.s. speed of the gas at \(800\,K\) will be:JEE Mains 2023 Easy
More PYQs from JEE Mains
- Assume that a drop of liquid evaporates by decrease in its surface energy, so that its temperature remains unchanged. What should be the minimum radius of the drop for this to be possible? The surface tension is \(T\), density of liquid is \(\rho\) and \(L\) is its latent heat of vaporizationJEE Mains 2013 Medium
- A \(25\,cm\) long solenoid has radius \(2\,cm\) and \(500\) total number of turns. It carries a current of \(15\,A.\) If it is equivalent to a magnet of the same size and magnetization \(\vec M\) ( magnetic moment/ volume), then \(\left| {\vec M} \right|\) isJEE Mains 2015 Medium