Charging by Induction- A spark or crackling sound emerges when our synthetic garments or sweaters are removed from our bodies, especially in dry weather. This is virtually unavoidable with feminine apparel, such as polyester sarees. Lightning, in the sky during thunderstorms, is another case of electric discharge. It is an electric shock always felt while opening a car door or grabbing the iron bar of a bus after sliding out of our seats.
What is Induction?
The cause of these sensations is the discharge of electric charges that have collected as a result of rubbing insulating surfaces. This is due to static electricity generation. Anything that does not have movement or change with time is referred to as static. The study of forces, fields, and potentials coming from static charges is known as Electrostatics.
Electrical neutrality refers to the presence of an equal amount of positive and negative charges in most bodies. To charge a neutral body, the balance of positive and negative charges has to be changed. The methods of altering the charge balance of a neutral body are:
- Friction
- Conduction
- Induction
Charging by Friction
The charging by friction method includes rubbing one particle against another, causing electrons to move from one surface to the next. This procedure can be used to charge insulators.
Charging by friction
- Different types of atoms and atom combinations in material objects give rise to various electrical characteristics.
- Electron affinity is a property that describes a substance’s affinity for electrons.
- Materials with high electron affinity strongly attract electrons.
- Turboelectric charging, or charging by friction, relies on electron affinity.
- For example, rubbing a rubber balloon with animal fur brings their atoms close together, causing their electron clouds to interact.
- Rubber atoms, with a stronger affinity for electrons, steal them from the fur, leading to both materials becoming charged.
- Similarly, when two glass rods rubbed with wool or silk cloth are brought together, they repel each other, along with the strands of cloth.
- However, the glass rod and the cloth are attracted to each other due to their differing electron affinities.
Charging by Conduction
- Charging by conduction occurs when a charged particle comes into contact with a neutral conductive medium.
- . Charges are transmitted from the charged substance to the neutral conductor. This approach can be used to charge conductors.
Charging by Conduction.
- Conduction charging happens when a charged object touches a neutral object.
- For instance, if a positively charged aluminum plate contacts a neutral metal sphere, the sphere becomes charged.
- Electrons from the neutral sphere move towards the positively charged plate.
- This movement causes the sphere to acquire a positive charge.
- Consider the case of a negatively charged metal spherical being pressed against the top plate of a neutral needle electroscope. When the metal sphere makes contact with the neutral electroscope, it charges it.
- Finally, imagine that an uncharged physics scholar is standing on an insulating platform when a scholar comes into contact with a negatively charged Van de Graaff generator causes the neutral physics scholar to become charged.
- Each of these cases includes a charged object making contact with a neutral object. In contrast to induction charging, which involves bringing the charged object close to but never touching the object being charged, conduction charging entails physically connecting the charged object to the neutral object.
- Charging by conduction is sometimes known as charging by touch since it involves contact.
Charging By Induction
Induction charging is a charging method in which a neutral object is charged without actually touching another charged object. The charged particle is held near a neutral or uncharged conductive material that is grounded on a neutrally charged material. When a charge flows between two objects, the uncharged conductive material develops a charge with the polarity opposite that of the charged object.
(1) Charging by induction using a positively charged rod:
Charging by induction using a positively charged rod.
- Place two metal spheres, A and B, on insulating platforms and bring them together.
- Bring a positively charged rod close to one of the spheres, say A, but don’t let it touch it. The rod attracts the free electrons in the spheres. The rear surface of sphere B now has an excess of positive charge. Both types of charges are encased in metal spheres and are unable to escape. As a result, they live on the surfaces. The left surface of sphere A has a negative charge surplus, while the right surface of sphere B has a positive charge excess. On the left surface of A, not all the electron particles in the spheres have collected. Other electron particles are repelled by the negative charge that is building upon A’s left surface. Under the operation of the rod’s attraction force and the force of repulsion caused by the accumulated charges, equilibrium is achieved in a short period. The equilibrium situation is depicted in Fig. 1.4(b).
- Induction of charge is the name for the process, which occurs nearly quickly. The collected charges remain visible on the surface until the glass rod is held close to the sphere, as shown. When the rod is withdrawn, the charges are no longer affected by external forces and revert to their original neutral condition.
- As indicated in Figure separate the spheres by a modest distance while holding the glass rod near sphere A. (c). The two spheres are found to be charged in opposite directions and are attracted to each other.
- Take out the rod. As demonstrated in Figure the charges on spheres rearrange themselves (d). Separate the spheres completely now. As illustrated in Figure the charges on them are uniformly spread over them (e).
- The metal spheres will be equal and oppositely charged in this operation.
- This is known as induction charging. In contrast to charging through contact, the positively charged glass rod does not lose any of its charges.
(2) Charging by induction using a negatively charged rod:
Charging by induction using a negatively charged rod.
- Consider two metal spheres A and B, which are touching in the illustration. Take a charged rod that is negatively charged. When a charged rod is kept close to the spheres, the repulsion between the charged rod’s electrons and the spheres causes electrons in the two-sphere system to move away.
- The electrons from sphere A are transported to sphere B as a result. Sphere A becomes positively charged and sphere B becomes negatively charged due to electron migration.
- As a result, the entire two-sphere system is electrically neutral. As illustrated, the spheres are then separated (avoiding direct contact with the metal). When the charged rod is removed, the charge is redistributed throughout the spheres, as indicated in the diagram.
Differences between Electrostatic and Electromagnetic Induction.
| S. no. |
Electromagnetic Induction |
Electrostatic Induction |
|---|---|---|
| 1. | Without any electrical connection, the formation of emf in a conductor due to the rate of change of current in a neighboring conductor. | Without any physical contact, the collection or redistribution of electric charges in a body caused by a neighboring charged body. |
| 2. | It is effective across great distances. | It is effective across short distances. |
| 3. | It’s because of the rate of change in charge flow. | It’s because of static charges. |
| 4. | In conductors, the effect is strongest. | In insulators, the effect is strongest. |
| 5. | The cause for this is due to the electric fields of the charges. | The cause is magnetic fields caused by moving charges. |
Law of Conservation of Charge
A charge is a characteristic of matter that causes it to create and experience electrical and magnetic effects. The underlying idea behind charge conservation is that the system’s overall charge is conserved. It can be defined as follows:
According to the rule of conservation of charge, the total charge of an isolated system will always remain constant. At any two time intervals, any system that is not exchanging mass or energy with its surroundings will have the same total charge.
When two objects in an isolated system each have a net charge of zero and one of the body transfer one million electrons with the other, the object with the surplus electrons will be negatively charged, while the object with the fewer electrons will have a positive charge of the same magnitude.
The total charge of the system has never changed and will never change.
Properties of Electric Charges
Additivity of Charges:
- In a system with two point charges q1 and q2 the total charge is determined by algebraically adding q1 and q2 similar to how real numbers are added.
- For a system with n charges ( q1,q2,q3,…qn) the total charge is calculated as ( q1+ q2+q3…qn).
- Charge, like mass, possesses magnitude but lacks direction.
- Unlike mass, which is always positive, charge can be positive or negative.
- When adding charges to a system, specific conventions must be followed to indicate the sign of each charge.
Conservation of Charge:
- The rule of conservation of charge states that the total charge of an isolated system remains constant over time.
- In an isolated system not exchanging mass or energy with its surroundings, the total charge remains the same at any two time intervals.
- For example, if two objects in an isolated system each have a net charge of zero and one transfers one million electrons to the other, the object gaining electrons becomes negatively charged, while the one losing electrons becomes positively charged.
- However, the total charge of the system remains unchanged throughout the process.
- This demonstrates the principle of charge conservation, where the total charge of an isolated system is constant and does not change over time.
Quantization of Electric Charge:
- All available charges are integral multiples of a basic unit of charge designated by e. As a result, the charge q on a body is always given by:
q = ne
Where n is any positive or negative integer.
The charge that an electron or proton carries is the basic unit of charge. The charge on an electron is assumed to be negative, the charge on an electron is written as –e, while the charge on a proton is written as +e.
Sample Problems
Problem 1: How much positive and negative charge is there in a cup of water?
Solution:
Let us assume that the mass of one cup of water is 250 g. The molecular mass of water is 18 g. Thus, one mole (= 6.02 × 1023 molecules) of water is 18 g. Therefore, the number of molecules in one cup of water is (250/18) × 6.02 × 1023. Each molecule of water contains two hydrogen atoms and one oxygen atom, i.e., 10 electrons and 10 protons. Hence, the total positive and total negative charge has the same magnitude. It is equal to
(250/18) × 6.02 × 1023 × 10 × 1.6 × 10–19 C = 1.34 × 107 C.
Problem 2: Compare the nature of Electrostatic and Gravitational Forces.
Solution:
Between two huge masses, a gravitational force acts. However, an electrostatic force is activated when two charged bodies come into contact.
Similarities:
- These two forces are central forces.
- Follow the law of inverse squares.
- They’re both long-range forces.
- Both forces are naturally conservative.
Dissimilarities:
- In nature, electrostatic force can be both attractive and repellent. In nature, gravitational force can only be attractive.
- The material medium between two charges affects the electric force between them. The material medium between huge bodies has little effect on gravitational force.
- Electric forces are extremely powerful (approximately 10 38 times stronger) than gravitational forces.
Problem 3: Why does Coulombs’ force act between two charges only in the line joining their centers?
Solution:
Because of the fundamental features of electrical charge, this is the case. Charges that are similar repel each other. Charges that are diametrically opposed attract each other.
The force of attraction or repulsion between two charges will be directed in the direction so that the force does the least amount of work. As a result of this requirement, the action is directed along the straight line connecting the two charges, which is the shortest distance between them.
Problem 4: If 109 electrons move out of a body to another body every second, how much time is required to get a total charge of 1 C on the other body?
Solution:
In one second 109 electrons move out of the body. Therefore, the charge given out in one second is
1.6 × 10–19 × 109 C = 1.6 × 10–10 C.
The time required to accumulate a charge of 1 C can then be estimated to be
1 C / (1.6 × 10–10 C/s) = 6.25 × 109 s
= 6.25 × 109 / (365 × 24 × 3600) years
= 198 years.
Thus, to collect a charge of one coulomb, from a body from which 109 electrons move out every second, we will need approximately 200 years. One coulomb is, therefore, a very large unit for many practical purposes. It is, however, also important to know what is roughly the number of electrons contained in a piece of one cubic centimeter of material. A cubic piece of copper of side 1 cm contains about 2.5 × 1024 electrons.
Problem 5: Write the differences between electrostatic and electromagnetic induction.
Solution:
Following are the differences between electrostatic and electromagnetic induction:
S. no. Electromagnetic Induction
Electrostatic Induction
1. Without any electrical connection, the formation of emf in a conductor due to the rate of change of current in a neighboring conductor. Without any physical contact, the collection or redistribution of electric charges in a body caused by a neighboring charged body. 2. It is effective across great distances. It is effective across short distances. 3. It’s because of the rate of change in charge flow. It’s because of static charges. 4. In conductors, the effect is strongest. In insulators, the effect is strongest. 5. The cause for this is due to the electric fields of the charges. The cause is magnetic fields caused by moving charges.
Related article:
- Principle of Mathematical Induction
- Problems on Electromagnetic Induction
- Electric Charge and Electric Field – Electric Flux, Coulomb’s Law, Sample Problems
- Faraday’s Laws of Electromagnetic Induction
Charging by Induction – FAQs
What is charging by induction explain?
Charging by induction is a method of charging an object by bringing it near a charged object without direct contact.
Can induction cause repulsion?
No, induction itself does not cause repulsion between objects.
What is an example of static electricity induction?
The example of static electricity induction is when you rub a balloon against your hair. When you rub the balloon, it becomes negatively charged due to the transfer of electrons from your hair to the surface of the balloon. Your hair, in turn, becomes positively charged because it lost electrons.
What do you mean induction?
Induction in the context of static electricity refers to the process by which charges in a neutral object are redistributed in the presence of a charged object, without direct contact between them
How does induction work?
The copper coil beneath the cooktop produces electromagnetic energy, which heats up induction-compatible cookware directly, making induction cooking fast and even.