# Physics Questions and Answers – The Gravitational Constant

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “The Gravitational Constant”.

1. What is the value of universal gravitational constant?
a) 6.022 x 1023
b) 6.67 x 10-11 N m2/kg2
c) 1.602 x 10-19 C
d) 9.81 m/s2

Explanation: 6.022 x 1023 is the Avogadro number.
6.67 x 10-11 N m2/kg2 is the value of universal gravitational constant.
1.602 x 10-19 C is the charge of a proton.
9.81 m/s2 is the acceleration due to gravity on the surface of the earth.

2. The gravitational constant is an empirical constant.
a) True
b) False

Explanation: The gravitational constant is the value of the slope of the graph “gravitational force versus (product of masses) / (square of the distance between them). So, it is not a derived constant, but an empirical one.

3. The value of universal gravitational constant changes is which of the following medium?
a) Air
b) Water
c) Plasma
d) The gravitational constant is independent of the medium

Explanation: Since the gravitational constant is an empirical constant, it does not vary with the medium. Hence, the value of the gravitational constant is the same in any part of the known universe.

4. What are the dimensions of universal gravitational constant?
a) [M2L3T2]
b) [M-1 L3 T-2]
c) [M-1 L3 T2]
d) [M1 L3 T-2]

Explanation: N m2/kg2 are the units of universal gravitational constant.
N m2/kg2 = m3/ (kgs2)
= m3kg-1s-2
Hence, the dimensions are [M-1 L3 T-2].

5. The value of gravitational constant was first determined by _____
a) Albert Einstein
b) Isaac Newton
c) Henry Cavendish
d) Stephen Hawking

Explanation: The value of gravitational constant was first experimentally determined by Henry Cavendish in the year 1798. It is also known as the Cavendish Gravitational Constant.
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6. What apparatus did Henry Cavendish use in his experiment to determine the gravitational constant?
a) 1 bar, 1 small sphere and 1 large sphere
b) 1 bar, 2 small spheres and 2 large spheres
c) 2 bar, 1 small sphere and 2 large spheres
d) 2 bar, 2 small spheres and 1 large sphere

Explanation: Henry Cavendish used 1 bar, 2 small spheres and 2 large spheres in his experiment to determine the gravitational constant. By measuring the torque and angle of deflection produced due to the proximity of large spheres to the small ones, Henry Cavendish was able to determine the universal gravitational constant.

7. What material were the spheres made up of in Henry Cavendish’s experiment?
b) Steel
c) Iron
d) Wood

Explanation: Henry Cavendish used lead spheres in his experiment because lead was easily available at the time. Iron was also abundantly available. However, Henry Cavendish chose lead because it is denser than iron and the mass of lead is about 44% higher than that of iron for the same size of the sphere – this would lead to a larger gravitational force which is easier to measure.

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