Notion of Positive and Negative Potential Energy

Q. six equal charges of magnititude 5μ c are placed at the corners of regular hexagon of side 1m the potential at the centre of the hexagon i

Q. Consider a gold nucleus to be a sphere of radius 6.9 fermi in which protons and neutrons are distributed. Find the force of repulsion between two protons situated at largest separation. Why do these protons not fly apart under this repulsion?

Q.

A hollow metal sphere of radius 10 cm is charged such that the potential on its surface is 80 volt. The potential at the centre of the sphere is

1. zero

2. 80 volt

3. 800 volt

4. 8 volt

Q. Assertion :Electrons in the atom are held due to coulomb forces. Reason: The atom is stable only because the centripetal force due to Coulomb's law is balanced by the centrifugal force.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q.

Check that the ratio ke²/G m_em_p is dimensionless. Look up a Table of Physical Constants and determine the value of this ratio. What does the ratio signify?

Q.

An electron and a proton are getting attracted towards each other by the virtue of internal electrostatic attraction. In the process, assuming infinity as our reference point, the P.E of the proton-electron system-

1. Increases

2. Decreases

3. Remains the same
4. \N

Q. 70. If a body with charge Q is further charged with 2C then its energy is increased by 21%. Then what is Q?

Q. a regular hexagon of side 10 cm has a charge 5 microcolumb at each of its vertices .calculate th potential at the centre of the hexagon.

Q. Four point masses each of mass m are kept at four corners of a cube of side length ‘a’. Then

1. The gravitational potential energy of system is $=-\frac{3\sqrt{2}G{m}^2}{a}$
2. The gravitational potential energy of system is $=-\frac{4\sqrt{2}G{m}^2}{a}$
3. The magnitude of force on one of the particle due to the remaining masses is equal to $\frac{\sqrt{6}G{m}^2}{a^2}$
4. The magnitude of force on one of the particle due to others is equal to $\sqrt{\frac{3}{2}}\frac{G{m}^2}{a^2}$

Q. If the Change in Potential energy of a system of charges is negative then the system has a tendency to come closer and if the Change in Potential energy of a system of charges is positive then the system has a tendency to move apart.

1. True
2. False

Q.

Two point charges each $50\mu C$ are fixed on the y-axis. Another charged particle having charge Q1 and a mass 20 gm moving with a speed of $20m{s}^{-1}$. Find the speed of charged particle when it reaches the origin? Also, find the distance of particle when Kinetic energy is 0.

Q. When the separation between two charges is increased, the electric potential energy of the charges
(a) increases
(b) decreases
(c) remains the same
(d) may increase or decrease

Q. If separation between two-point charges decreases then electric potential energy of the system increases, whatever be the sign of charges. Yes or No?

Q. If the Change in Potential energy of a system of charges is negative then the system has a tendency to come closer and if the Change in Potential energy of a system of charges is positive then the system has a tendency to move apart.

1. True
2. False

Q.

Where will be the higher potential of a charged particle , near to the electric field or far away distance from the election field of a constant particle kept at a point?

Q. Two discharge tubes have identical material structures and the same gas is filled in them. The length of one tube is 10 cm and that of the other tube is 20 cm. Sparking starts in both the tubes when the potential difference between the cathode and the anode is 100 V. If the pressure in the shorter tube is 1.0 mm of mercury, what is the pressure in the longer tube?

Q.

Answer the following questions:

(a) Quarks inside protons and neutrons are thought to carry fractional charges [(+2/3)e ; (−1/3)e]. Why do they not show up in Millikan’s oil-drop experiment?

(b) What is so special about the combination e/m? Why do we not simply talk of e and m separately?

(c) Why should gases be insulators at ordinary pressures and start conducting at very low pressures?

(d) Every metal has a definite work function. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Why is there an energy distribution of photoelectrons?

(e) The energy and momentum of an electron are related to the frequency and wavelength of the associated matter wave by the relations:

E = hν, p =

But while the value of λ is physically significant, the value of ν (and therefore, the value of the phase speed νλ) has no physical significance. Why?

Q.

An electron and a proton are getting attracted towards each other by the virtue of internal electrostatic attraction. In the process, assuming infinity as our reference point, the P.E of the proton-electron system-

1. Increases

2. Decreases

3. Remains the same
4. First increase then decrease

Q. A beam consisting of protons and electrons moving at the same speed goes through a thin region in which there is a magnetic field perpendicular to the beam. The protons and the electrons
(a) will go undeviated
(b) will be deviated by the same angle and will not separate
(c) will be deviated by different angles and hence will separate
(d) will be deviated by the same angle but will separate

Q. If the Change in Potential energy of a system of charges is negative then the system has a tendency to come closer and if the Change in Potential energy of a system of charges is positive then the system has a tendency to move apart.

1. False
2. True

Q.

An electron and a proton are getting attracted towards each other by the virtue of internal electrostatic attraction. In the process, assuming infinity as our reference point, the P.E of the proton-electron system-

1. Increases

2. Decreases

3. Remains the same
4. First increase then decrease

Q.

An electron and a proton are getting attracted towards each other by the virtue of internal electrostatic attraction. In the process, assuming infinity as our reference point, the P.E of the proton-electron system-

1. Increases

2. Decreases

3. Remains the same
4. First increase then decrease

Q. Four point masses each of mass m are kept at four corners of a cube of side length ‘a’. Then

1. The gravitational potential energy of system is $=-\frac{3\sqrt{2}G{m}^2}{a}$
2. The gravitational potential energy of system is $=-\frac{4\sqrt{2}G{m}^2}{a}$
3. The magnitude of force on one of the particle due to the remaining masses is equal to $\frac{\sqrt{6}G{m}^2}{a^2}$
4. The magnitude of force on one of the particle due to others is equal to $\sqrt{\frac{3}{2}}\frac{G{m}^2}{a^2}$

Q. Charges q are placed at the corners of a cube of side a. Find the potential at a) the centre b) centre of face c) mid point of an edge d) if q = 5 uc & a = 1 m , how much energy will be required to add 1 uc at one of the corners?

Q.

The gravitational attraction between electron and proton in a hydrogen atom is weaker than the coulomb attraction by a factor of about 10⁻⁴⁰. An alternative way of looking at this fact is to estimate the radius of the first Bohr orbit of a hydrogen atom if the electron and proton were bound by gravitational attraction. You will find the answer interesting.

Q.

Check that the ratio ke²/G m_em_p is dimensionless. Look up a Table of Physical Constants and determine the value of this ratio. What does the ratio signify?