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A point charge ‘q’ is kept at each of the vertices of an equilateral triangle having each side ‘a’…

Physics202012 marksShort answer
(A)(i)[1.0]
A point charge ‘q’ is kept at each of the vertices of an equilateral triangle having each side ‘a’. Total electrostatic potential energy of the system is:
  • (a)$\left(\frac{1}{4\pi\varepsilon_0}\right) \frac{3q^2}{a^2}$
  • (b)$\left(\frac{1}{4\pi\varepsilon_0}\right) \frac{3q}{a}$
  • (c)$\left(\frac{1}{4\pi\varepsilon_0}\right) \frac{3q^2}{a}$
  • (d)$\left(\frac{1}{4\pi\varepsilon_0}\right) \frac{3q}{a^2}$
(A)(ii)[1.0]
Curie temperature is the temperature above which:
  • (a)a ferromagnetic substance behaves like a paramagnetic substance.
  • (b)a paramagnetic substance behaves like a diamagnetic substance.
  • (c)a ferromagnetic substance behaves like a diamagnetic substance.
  • (d)a paramagnetic substance behaves like a ferromagnetic substance.
(A)(iii)[1.0]
In an astronomical telescope of refracting type:
  • (a)Objective should have small focal length.
  • (b)Objective should have large focal length.
  • (c)Eyepiece should have large focal length.
  • (d)Both objective and eyepiece should have large focal length.
(A)(iv)[1.0]
In photoelectric effect experiment, the slope of the graph of the stopping potential versus frequency gives the value of:
  • (a)$\frac{h}{e}$
  • (b)$h$
  • (c)$\frac{e}{h}$
  • (d)$\frac{hc}{e}$
(A)(v)[1.0]
In a nuclear reactor, cadmium rods are used as:
  • (a)Control rods
  • (b)Fuel rods
  • (c)Coolant
  • (d)Moderator
(B)(i)[1.0]
State Gauss’ theorem.
(B)(ii)[1.0]
A metallic wire having a resistance of $20\ \Omega$ is bent in order to form a complete circle. Calculate the resistance between any two diametrically opposite points on the circle.
(B)(iii)[1.0]
How can a moving coil galvanometer be converted into a voltmeter?
(B)(iv)[1.0]
Write Biot-Savart’s law in vector form.
(B)(v)[1.0]
What is the phase difference between any two points lying on the same wavefront?
(B)(vi)[1.0]
Name the physical principle on the basis of which optical fibres work.
(B)(vii)[1.0]
What is Pair production?

Answer

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Electrostatic Potential, Potential Energy and Capacitance

From ISC 2020 Physics Paper 1, question 1.