Chapter 4 Flashcards
What is an electric charge?
When you rub a balloon on your head for some time, pulling the balloon away attracts some hairs to it, causing them to essentially standup against gravity.
The property of attraction or repulsion between substances is due to a property called electric charge. It is an inherent quality, its S.I unit is Coulomb (C).
types of electric charges and the experiments used to determine their properties
Positive and negative. Atoms have positive charges in the form of protons in the nucleus; negative charges are called electrons that revolve around the nucleus. Neutral particles are called neutrons.
Glass rods rubbed with silk brought together while one is suspended by a thread repel each other. Rubber rods rubbed with animal fur experience the same, while one rubber rubbed with animal fur and one glass rod rubbed with silk attract.
same charges repel, opposites attract.
What conclusions were derived from the rods experiment?
A charge is a basic property of materials due to which they attract or repel each other.
There are two types of charges between two materials.
same charges repel, opposites attract.
why are paper pieces attracted by balloon when rubbed with hair
The balloon is charged by rubbing it on your hair. When you put it near a neutral object (paper, Styrofoam or puffed rice cereal), the electrons in the object repel away from the balloon and the protons are attracted to the balloon. This movement of the electrons causes an electrostatic attraction between the opposite charges.
when robbing a plastic rod with fur, do both bodies acquire equal but opposite charges/
When you rub a plastic rod with fur, the rod might become positively charged, and the fur negatively charged. In this case, the charges are not equal but opposite.
what would happen if a neutral glass rod is brought near a positively charged glass rod
When a neutral glass rod is brought near a positively charged glass rod, the electrons in the neutral rod will be attracted towards the side closer to the charged rod due to the positive charge.
what is electrostatic charge?
A change in the electrical charge distribution due to the influence of nearby charges is called an electrostatic charge.
what is an electroscope?
A device used for detecting and testing the nature and magnitude of charge on a body. A simple one consists of a metal bar with an unchanged metallics disc at the upper end, thin gold leaf or any metal attached at the lower half enclosed with an insulated housing.
How does an electroscope work?
When we touch the uncharged disc with a negatively charged plastic rod, its excess electrons will be transferred onto the disc, spreading throughout the metal rod, repelling the flexible leaf bcuz of the similar charge on the metal rod. Similarly, if a +charged rod is brought near the disc, electrons will be attracted from the electroscope, leaving it net+, causing the foil to rise again.
But to test the nature of the charge, we charge the electroscope with either - or + charge. Id the same charge is added to the metal disc, metal leaf divergence will increase with the same charge or decrease on opposite charge.
What is coulomb’s law
Charles Coulomb provided an experimental law to explain the magnitude of electrostatic force between the charges in 1785.
statement: - or + electrostatic forces between two point charges is;
Directly proportional to the product of charges Fe ∝q1q2
Inversely proportional to the square of the separation between charges Fe∝ 1/r^2
After combining both, Fe∝ q1q2/r^2
replacing ∝ with = and adding a constant Fe= k q1q2/r^2
Where k is coulomb’s constant, value dependent upon the medium between charges. Law is only true for charges very small compared to the distance between them.
Nature of coulomb’s force
For the same, repulsive charges, both will repel each other with the force whose magnitude is given by
Fe= k q1q2/r^2.
For opposite, attracting charges, magnitude of force is also given by that equation.
Repulsive force will be positive (++ = +) and attractive force will be negative (+- = -).
Direction: it’s a vector, so its both magnitude and direction, with the magnitude is given by the same equation as above.
Direction of force will be along the line of joining charges.
What is electric field intensity?
electrostatic force per unit charge (unit positive q0 = + 1 C) when it is within the influence of an electric field. E= Fe/q0.
SI unit is N/C
what is the direction of electric field intensity?
electric field intensity is also a vector quantity having both magnitude and direction. The direction of electric field intensity at a point will be the direction of force on a positive test charge at that point.
What are electric field lines?
To visualize an electric field around a source charge, the direction of force on a positive test charge is represented by a line showing the direction of the electric field intensity at that point.
Introduced by Michael Faraday, they are imaginary. For positive charges, lines show direction moving away from positive charge while it is opposite for negative charge.
What is electrical potential?
amount of work done in bringing a unit of positive charge from infinity to that point inside an electrical field.
(page 88)
what are some applications of electrostatics?
Electrostatic precipitator and dust extraction; to reduce air pollution, coal burning power stations use electro static precipitation phenomena to extract dust from chimney smoke. Dust mixed with air enters a device across a positively charged mesh, then pass a negatively charged mesh. The opposite forces between the negative and positive particles in the air cause the particles to precipitate out on the surface of the mesh.
Electro painting; how cars are often painted by giving the nozzle of the paint machine an opposite charge than the material of the car. Charge can also be applied to the paint directly. Once it is applied, it gains static electricity while on the move, opposites attract so the paint adheres to the car.
The Problem with electrostatics in relation to electricity
large quantities of electric charge separation occurring within a thundercloud cause lightning. Charged by the friction between water and air molecule. These charges induce opposite charges from ground objects, giving rise to a strong electric field between them, causing a sudden strike of lightning.
Conductors are used on top of large buildings to redirect lightning strikes by providing a steady discharge path for negative charge in the air.
The Problem with electrostatics in relation to electricity
Static electricity causes a lot of fires and explosions, which can occur due to an excessive build-up of electric charges produced by friction. This can occur in gasoline being pumped into the oil tank of the car or container.
To prevent this from happening, steel chains are attached to another end that reaches the ground to allow static energy to discharge into the ground.
what is a capacitor?
Device used to store electrical charges of electrical energy is called capacitor. Parallel plat capacitors consist of two metal plates placed parallel to each other, distance d apart.
The medium between can be any insulator called dielectric. The capacitors are charged by connecting one plate to the positive terminal of the battery and the other with the negative terminal of the batter.
The potential difference between capacitor plates will be equal to applied voltage, increasing the voltage will increase charge storage, but only to a certain limit. If voltage is further increased, the capacitor will be damaged and hence will loose all its charges. The limit is usually written on the capacitor itself.
What is the capacitance of a capacitor?
The charge stored on the plates of a capacitor depends upon the applied voltage. Greater the applied voltage, greater will be the stored charge.
Q= CV → C= Q/V
The ability or the capacity of a capacitor to store a charge per unit applied voltage is called the capacitance of a capacitor.
What is the unit of capacitance
SI unit of capacitance is farad (F), which is defined as the capacitance of a capacitor will be 1 F if 1 C of charge is stored on the plates when the applied voltage is 1V.
1 microfarad = 1μF=10^-6F
1 nanofarad=1nF=10^-9F
1 picofarad = 1pF = 10^-12F
rub a plastic ruler on your hair, when placed near water, the stream is deflected. Why?
When we rub a plastic ruler with our hair, friction is produced which charges the ruler. Now, if we place this charged ruler near running water, the stream is deflected because of the electrostatic force between the charged ruler and the polar water molecules.
two identical spheres have the same mass. When we charge them both oppositely, will they still have the same masses or different masses?
No both spheres will have slightly different masses after being charged oppositely. When one sphere is given a positive charge, it loses electrons, which decreases its mass. When the other sphere is given an equal negative charge, it gains electrons, which increases its mass.
