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Chapter 12 Electrostatics Physics 12th Class Punjab Short Questions

Question No. 1 - Why do the electrons tend to go to region of high potential?

Answer No. 1 - We know that the electrons are negatively charged particles. So, when they are put inside an electric field they tend to go the region of high potential from the region of low potential.

Question No. 2 - How can you identify that when plate of capacitor is positively charged?

Answer No. 2 - For the identification of positively charged plate of a capacitor golf leaf electroscope is used for this purpose the plate of capacitor is brought near the positively charged disc of electroscope. If the divergence of the gold leaves increase then the capacitor will be positively charged and vice versa.

Question No. 3 - What is the effect of medium between the charges upon coulombs force?

Answer No. 3 - If an insulating material i.e direction is places between the charges, it will reduce the electrostatic force as compared to free space by factor called relative permittivity.

Question No. 4 - How can you identify that which plate of a capacitor is positively charged?

Answer No. 4 - Gold leaf electroscope is used, To check the polarity, disc of positively charged electroscope is brought close to the capacitor plate. If the divergence of gold leaves increases; the plate is positively charged and vice versa.

Question No. 5 - Write down two difference between electric and gravitational force.

Answer No. 5 - Differences: Electrical force is might be attractive as well as repulsive while the gravitational force is only attractive. Electrostatics force is medium dependent while the gravitational force is not.

Question No. 6 - Describe the force on positive charge when placed between parallel plates with opposite and equal charges.

Answer No. 6 - When a positive point charge is placed between parallel plates with opposite but equal amount of charge, then electric field intensity due to one plate is equal in magnitude but in same direction of the electric field intensity due to the other plate. So the value of resultant electric field intensity is non-zero. Hence the point charge will be accelerated towards negative plate.

Question No. 7 - Is it true that Gausss law states that the total number of lines of forces crossing any closed surface in the outwards direction is proportional to the net positive charged enclosed within surface?

Answer No. 7 - Yes the above statement is true. The total number of lines of force crossing any close surface in the outwards directions means electric flux.

Question No. 8 - Distinguished between electric field and field intensity.

Answer No. 8 - Electric Field: The space or region around the charge in which it exerts its electric force on other charges is called electric field.

Question No. 9 - Give the statement of Gausss law.

Answer No. 9 - It states that the total electric flux through any closed surface is equal to 1/e times the total charged encloses in it.

Question No. 10 - Does the total flux depend upon the shape or geometry of the closed surface?

Answer No. 10 - No, the total flux does not depend upon the shape or geometry of the closed surface. It depends upon medium and charge enclosed.

Question No. 11 - Define Time constant for RC Circuit.

Answer No. 11 - The time required by the capacitor to deposit 0.63 times the equilibrium charge q is called time constant. The product of R and C has the dimensions of time. So this product is known as time constant.
t=RC

Question No. 12 - Do electrons tend to go region of high potential or low potential?

Answer No. 12 - Electrons tend to go to a region of high potential from low potential because electrons are negatively charged.

Question No. 13 - What is meant by EEG and ERG?

Answer No. 13 - Electroencephalography: is usually applied over human brain to check its abnormal behaviour by the use of electrical energy. For this electrodes are connected to the selected portion of the head and the corresponding response is seen graphically through the screen of a recording device.

Question No. 14 - Define electric polarization and electric dipole.

Answer No. 14 - When dielectric is placed between the plants of capacitor, positive and negative charge of its molecules displace from their position. Positive charges are attracted towards negative plates and negative charges towards positive plate, dipoles are formed. This process is called polarization. Two equal and opposite charges separated by a small distance is called dipole.

Question No. 15 - Define electric potential and give its SI units.

Answer No. 15 - The electric potential at any point in an electric field is equal to work done in bringing a unit positive charge from infinity to that point keeping it in equilibrium. Its SI unit is Volt V.

Question No. 16 - Define electric flux. Write its SI units.

Answer No. 16 - The number of the field lines passing through a certain element of area is known as electric flux through that area. Its SI units is Nm2C-1.

Question No. 17 - A point charge move rectilinear path in an electric field. Explain.

Answer No. 17 - If a point charge q of mass m is placed at any point in the field in the point, it will follow straight or rectilinear path along the field line due to repulsive force.

Question No. 18 - What is Potential Gradient?

Answer No. 18 - The quantity gives the maximum value of rate of change of electric potential in magnitude and direction with respect to distance. It is known as potential gradient.

Question No. 19 - Define electrostatics and electric force.

Answer No. 19 - Electrostatics: The branch of physics which deals with the study of stationary charges is called electrostatics. Electric Force: The force which holds the negative and positive charges that make up atoms or molecule is called electric force.

Question No. 20 - What is strength of electric field inside a hollow charged sphere and why?

Answer No. 20 - The strength of electric field inside a hollow charge is zero inside a hollow charge sphere q=0.

Question No. 21 - Is E is necessary zero inside a charged rubber balloon if balloon is spherical?

Answer No. 21 - Yes, E is necessarily zero inside a charged rubber balloon if balloon is spherical.

Question No. 22 - What is photo conductor?

Answer No. 22 - A material which behaves as an insulator when it is in dark and becomes conductor when it is exposed to light is known as photo conductor.

Question No. 23 - Describe the force or forces on a positive point charge when placed between parallel plate with similar and equal charges.

Answer No. 23 - When a positive point charge is placed between parallel plates with similar and equal charges, then the electric field intensity due to one plate is equal in magnitude but opposite in direction of electric intensity due to other plate. So the value of resultant electric field intensity E is zero. Hence the net force on the positive charge is zero. Thus is will remain at rest.

Question No. 24 - If a point charge q of mass is released in a non-uniform electric field with field lines pointing in the same directions will it make rectilinear motion?

Answer No. 24 - If a point charge q of mass m is placed at any point in the field, it will follow straight or rectilinear path along the field line due to repulsive force.

Question No. 25 - How sharks looks their prey?

Answer No. 25 - Sharks have special organs,called the ampule of Lorentzian that are very sensitive to electric field and can detect potential difference of the order of nano volt and can locate their prey very precisely.

Question No. 26 - What is capacitor? Define the capacitance.

Answer No. 26 - Capacitor is a device used to store charge. Capacitance is a measure of ability of capacitor to store charge.

Question No. 27 - State coulombs law.

Answer No. 27 - It states that the force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charge and inversely proportional to the square of the distance between them.

Question No. 28 - Electric lines of force never cross why?

Answer No. 28 - Electric lines of force never cross each other. This is because that electric field line has only one direction at any given point. If the lines cross, electric field lines could have more than one direction which is not possible.

Question No. 29 - Write two properties of electric field.

Answer No. 29 - 1. Electric field line originate from positive charge and
end om negative charges.
2. The tangent to a field line at any point gives the
direction of the electric field intensity at the point.

Question No. 30 - What depend on the slow or fast charging and discharging of a capacitor?

Answer No. 30 - How fast or how slow the capacitor is charging or discharging depends upon the products of the resistance and the capacitance called time constant. Capacitor is charged or discharged rapidly when RC is small.

Question No. 31 - What is time constant?

Answer No. 31 - The time required by the capacitor to deposit 0.63 times the equilibrium charge Lois called time constant. The product of R and C has the dimensions of time. So, this product is known as time constant.

Question No. 32 - Define electron volt.

Answer No. 32 - It is defined as The amount of energy acquired or lost by an electron when it is displaced across two points having potential difference of one volt. It is measure on electrons volts.

Question No. 33 - Define electric intensity and give its unit.

Answer No. 33 - The electrostatic force per unit test charge, at a specific point in the electric field is called electric field intensity. Its unit is NC-1.

Question No. 34 - What is electric potential energy and electric potential difference?

Answer No. 34 - Electric Potential Energy: The energy is acquired by unit positive charge in carrying it from one point to the other against the electric field keeping it in electrostatic equilibrium is called as electric potential energy. It is the energy stored in the charge q because of its position in an electric field. It is measured in joules.

Question No. 35 - Define xerography and photo conductor.

Answer No. 35 - Xerograph is a photocopying process, It is taken from the Greek word "xeros" and "graphos" when mean dry writing.
Photo conductor is an insulator in the dark and becomes a conductor when exposed to light.

Question No. 36 - Suggest a method shield an apparatus from electric field even when it is to be kept in the region where electric field is present.

Answer No. 36 - An apparatus will be shielded from electric field when it is kept inside the metallic box, so that the charge will only reside on the outer surface of the container. It is in accordance with Gauss law.

Question No. 37 - Center of planetary system is oppositely charged to the rest of planets. How orbits of planets would be modified?

Answer No. 37 - It would add or subtract the gravitational force if the charge was large enough and the sun was charged. So the radius of the orbits would be changed.

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