M5 Physics Electric Feids 2nd Sem

Electric Forces and Fields

Electric Charge

Learning Objectives:

• Understand the basic properties of electric charge.

• Differ between conductors and insulators.

• Distinguish between charging by contact, charging by induction, and charging by polarization.

Electric Charge

When this happens, one object becomes negatively charged (balloon) and the other becomes positively charged (hair).

Electron is a negatively charged subatomic particle of an atom

Located in outermost position and very light

Electron can jump between atoms, creating a flow of electricity

It makes new place negative and the place where it leaves becomes positive charge as it lose electron

We have two type of charge

Positive and Negative

Charge will produce a force that will push or pull each other

Between same charge, it repel and different charge attracts

Positively charged doesn't mean no negative charge, just it is less amount than positive.

​

Some text here about the topic of discussion

Positively or negatively charged object

Can be produced by two method

1. Rubbing two object together: One will lose positive and one will lose negative.

2. Induction: Put a charged object near a neutral that connected to earth​, then cut it.

Electric charge is conserved.

Electric charge is conserved in this process; no charge is created or destroyed. This principle of conservation of charge is one of the fundamental laws of nature.

Electric charge is quantized.

In 1909, Robert Millikan conducted an experiment to study electric charge by observing the motion of tiny oil droplets between two charged metal plates. He found that the charge on objects is always a multiple of a fundamental unit of charge, symbolized by "e." This discovery showed that electric charge is quantized, meaning it exists in discrete amounts like ±e, ±2e, and so on. The value of "e" is approximately 1.602 × 10¹⁹ coulombs (C), which is the charge of an electron.

Transfer of Electric Charge

Materials are classified based on how they transfer electric charge:

1. Conductors (e.g., copper, aluminum): These allow electric charges to move freely.

2. Insulators (e.g., glass, rubber, plastic): These do not allow electric charges to move freely.

3. Semiconductors: These have properties between insulators and conductors. In their pure state, they are insulators, but adding impurities can improve their ability to conduct electricity. Silicon and germanium are examples.

4. Superconductors: These materials have zero electrical resistance at certain temperatures and can conduct electricity without any loss.

Insulators and conductors can both be charged by contact.



When objects like a balloon and hair are rubbed together, they become charged through a process called "charging by contact." For example, rubbing a glass rod with silk or a rubber rod with wool causes them to become oppositely charged and attract each other. When two like-charged objects, such as two glass rods or two rubber rods, are rubbed, they repel each other.

Though metals like copper may not seem to become charged in similar experiments, they can be charged by contact. When a copper rod is rubbed with wool while held by an insulating handle, it can attract or repel other charged rods. This occurs because the insulating handle prevents the charge from flowing to the ground, allowing the rod to remain charged.

​Electric Force

Learning Objectives:

• Calculate electric force using Coulomb’s law.

• Compare electric force with gravitational force.

• Apply the superposition principle to find the resultant force on a charge and the position at which the net force on a charge is zero.

​Coulomb's Law describes the electric force between two charged objects. This force can be either attractive (between opposite charges) or repulsive (between like charges). The force's magnitude depends on both the amount of charge on the objects and the distance between them.

Charles Coulomb, in the 1780s, determined that the electric force is:

1. Proportional to the product of the charges: if one charge doubles, the force doubles. If both charges double, the force increases by a factor of four.

2. Inversely proportional to the square of the distance between the charges: if the distance between the charges is halved, the force increases by a factor of four.

• F_e is the electric force

• q₁​ and q_2​ are the charges,

• r is the distance between the charges

• k_C​ is the Coulomb constant

  (8.99 × 10⁹ N·m²/C²)

​F_g is the gravitation force,

• m_1​ and m₂​ are the mass points

• r is the distance between mass points

• G is gravitational constant

  (6.67 x 10^-11 N.m²/Kg² )

​Forces are equal when charged objects are in equilibrium.

According to Newton's first law, an object in equilibrium experiences no net external force. In electrostatic situations, equilibrium occurs when the net electric force on a charge is zero. This happens when the electric forces from two charges balance each other out.

Electric force is a field force, meaning it acts on objects without physical contact, similar to gravitational attraction.




However, electric forces can be either attractive or repulsive, unlike gravitational forces, which are always attractive.

Electric Fields

Learning Objectives:

• Calculate electric field strength.

• Draw and interpret electric field lines.

• Identify the four properties associated with a conductor in electrostatic equilibrium.

Electric Fields

Attract and Repel happens, but only in field

Electric field is the region where a charge experiences electric force.

Outside electric field, no force, no attract / repel.​

The electric field for positive is outward line of the charge.

The electric field for negative is inward line of the charge.

M​ore lines represents stronger field and a stronger force inside it.

Negative

Positive

Example of electric field drawing

Electric field reaction

Between two charges (same or different)

​Electric field strength depends on charge and distance.

Electric Potential

• Learning Objectives:​

• Distinguish between electrical potential energy, electric potential, and potential difference.

• Solve problems involving electrical energy and potential difference.

• Describe the energy conversions that occur in a battery.

​Electrical potential energy: potential energy associated with a charge due to its position in an electric field. Unlike gravitational potential energy, electrical potential energy results from the interaction of two objects’ charges, not their masses.

​Electrical potential energy can be associated with a charge in a uniform field.

A uniform field is a field that has the same value and direction at all points. Assume the charge is displaced at a constant velocity in the same direction as the electric field.

​The negative sign indicates that the electrical potential energy will increase if the charge is negative and decrease if the charge is positive. As with other forms of potential energy, it is the difference in electrical potential energy that is physically important.

Electric potential is the work that must be performed against electric forces to move a charge from a reference point to the point in question, divided by the charge.
Potential Difference is the work that must be performed against electric forces to move a charge between the two points in question, divided by the charge.

A potential difference is a change in electric potential.

​The potential at a point is the result of the fields due to all other charges near enough and large enough to contribute force on a charge at that point. In other words, the electric potential at a point is independent of the charge at that point.

The potential difference in a uniform field varies with the displacement from a reference point.

​Keep in mind that d is the displacement parallel to the field and that motion perpendicular to the field does not change the electrical potential energy.

Multiple Choice

How many charges exist?

• 1

• 2

• 3

Multiple Choice

Which one is the method to produce charged object without touching?

• Rubbing

• Induction

Multiple Choice

Between negative charge and negative charge, what happen?

• Attract

• Repel

• Nothing

Capacitance & Dielectrics

• Learning Objectives:​

• Relate capacitance to the storage of electrical potential energy in the form of separated charges.

• Calculate the capacitance of various devices.

• Calculate the energy stored in a capacitor.

​https://www.youtube.com/watch?v=f_MZNsEqyQw

A capacitor is a device that stores electrical potential energy, with applications such as tuning radio frequencies, preventing ignition system sparks, and powering electronic flashes. A common type, the parallel-plate capacitor, consists of two metal plates separated by a small gap. When connected to a battery or other voltage source, charges are transferred between the plates until the potential difference across them matches the source's voltage.

Capacitance is the ratio of charge to potential difference. The ability of a conductor to store energy in the form of electrically separated charges is measured by the capacitance of the conductor. Capacitance is defined as the ratio of the net charge on each plate to the potential difference created by the separated charges.

​Capacitance the ability of a conductor to store energy in the form of electrically separated charges.

In a parallel-plate capacitor, inserting a dielectric material (such as air, rubber, or glass) between the plates increases the capacitance.

The dielectric aligns its molecules with the electric field, creating surface charges that reduce the effective charge on the capacitor plates. This allows the capacitor to store more charge and energy for a given potential difference.

A charged capacitor stores electrical potential energy because it requires work to move charges through a circuit to the opposite plates of a capacitor. The work done on these charges is a measure of the transfer of energy.

Multiple Choice

A ________ is a device that stores electrical potential energy, with applications such as tuning radio frequencies, preventing ignition system sparks, and powering electronic flashes.

• insulator

• capacitor

• inductor

Multiple Select

Choose the following types of capacitor.

• bipolar

• paper

• electrolytic

• polyester

• ceramic

Multiple Choice

This aligns its molecules with the electric field, creating surface charges that reduce the effective charge on the capacitor plates and allows the capacitor to store more charge and energy for a given potential difference.

• electric field

• dielectric

• capacitor

Multiple Select

In a parallel-plate capacitor, inserting a dielectric material (such as ____, ______ or _____) between the plates increases the capacitance.

• glass

• rubber

• air

• silver

Multiple Choice

The ability of a conductor to store energy in the form of electrically separated charges.

• electric field

• dielectric

• capacitor

• capacitance

Multiple Choice

The formula for solving capacitance is _______.

• $$C\ =\ \frac{Q}{\Delta V}$$

• $$C\ =\ \frac{\Delta V}{Q}$$

• $$C\ =\ ^{Q\Delta V}$$

Multiple Choice

The formula for solving the electric potential energy stored in a charged capacitor.

• $$C\ =\ \frac{Q}{\Delta V}$$

• $$C\ =\ \frac{\Delta V}{Q}$$

• $$C\ =\ ^{Q\Delta V}$$

• PE_{elastic =} $$\frac{1}{2}Q\left(\Delta V\right)^2$$

Nature of Conductors

​The nature of conductors is defined by their ability to allow the free movement of charge carriers, such as electrons or ions, within them.

1.​Free Charge Carriers:

In metals, free electrons act as charge carriers. They are not bound to individual atoms and can move freely through the material.

In ionic conductors, such as electrolytes, charged ions (positive and negative) serve as the charge carriers.

2.Low Resistance:
Conductors have low electrical resistance, making it easy for electric currents to flow through them. Metals like copper, silver, and aluminum are excellent conductors due to their high density of free electrons.

3.Electric Field Distribution:

Inside a conductor in electrostatic equilibrium, the electric field is zero. This occurs because free electrons rearrange themselves to cancel out any internal field.

4.Thermal Conductivity:
Conductors are also good at transferring heat, as the free electrons can transport thermal energy efficiently.

5.Response to Potential Difference:
When a potential difference (voltage) is applied, an electric field is established, causing the free charge carriers to move and create an electric current.

Multiple Choice

The SI unit for capacitance is _____.

• Coulombs

• Farad

• Volts

Multiple Choice

1 Farad = _______.

• Coulomb/Volt

• Volt/Coulomb

• Volts

Multiple Choice

$$1\mu F\ =\ \ \ \ \ \ F$$

• 1 x 10 ^-9

• 1 x 10 ^-6

• 1 x 10 ^-12

Multiple Choice

$$1\rho F\ =\ \ \ \ \ \ F$$

• 1 x 10 ^-9

• 1 x 10 ^-6

• 1 x 10 ^-12

Multiple Choice

Conductors have low ____________, making it easy for electric currents to flow through them.

• electrical capacitance

• electrical potential energy

• electrical resistance

• electric potential

Multiple Choice

In metals, free electrons act as _________.

• electrical capacitance

• charge carriers

• electrical resistance

• electric potential

Multiple Choice

Ionic conductors, such as electrolytes, ___________ serve as the charge carriers.

• electrical capacitance

• charge carriers

• electrical resistance

• charged ions (positive and negative)

Multiple Choice

The nature of a conductor where in free electrons rearrange themselves to cancel out any internal field.

• Electric Field Distribution

• Thermal Conductivity

• Free Charge Carriers

• Low Resistance

Multiple Choice

The nature of a conductor where they are considered good at transferring heat, as the free electrons can transport thermal energy efficiently.

• Electric Field Distribution

• Thermal Conductivity

• Free Charge Carriers

• Low Resistance

Multiple Choice

When a potential difference (voltage) is applied, an electric field is established, causing the free charge carriers to move and create an ________.

• electromagnectic field

• electric field

• electric potential energy

• electric current

​Current
and
Resistance

Current and Resistance

Learning Objectives:​

• Describe the basic properties of electric current, and solve problems relating current, charge, and time.

• Distinguish between the drift speed of a charge carrier and the average speed of the charge carrier between collisions.

• Calculate resistance, current, and potential difference by using the definition of resistance.

• Distinguish between ohmic and non-ohmic materials, and learn what factors affect resistance

https://www.youtube.com/watch?v=AkWyNFPpRE0

In a conductor, free electrons move randomly when in electrostatic equilibrium. When a potential difference is applied, an electric field forms, setting the electrons into motion and creating a current. Their motion is not straight but follows a zigzag path due to collisions with vibrating metal atoms. These collisions increase the conductor's temperature.

The net motion of electrons along the conductor, opposite to the electric field, is called drift velocity.

​Ohm's Law

​

Resistance

​Resistance is a force that counteracts the flow of electricity. Resistance influences the flow of electricity.

Multiple Choice

It is a law stating that electric current is proportional to voltage and inversely proportional to resistance.

• electromagnectic field

• Electricity

• Ohm's Law

• electric current

Multiple Choice

The rate at which electric charges pass through a given area.

• electromagnectic field

• electric field

• electric potential energy

• electric current

Multiple Choice

What is the formula for solving electric current?

• $$I=\frac{\Delta t}{\Delta Q}$$

• $$I=\frac{K_c}{\Delta t}$$

• $$I=\frac{\Delta Q}{\Delta t}$$

Multiple Choice

A current exists whenever there is a net movement of ______ through a medium.

• electric wire

• electric current

• electric charge

Multiple Choice

When a potential difference is applied, an electric field forms, setting the electrons into motion and creating a current. Their motion is not straight but follows a ______ path due to collisions with vibrating metal atoms.

• slope

• straight line

• Zigzag

Multiple Choice

The net motion of electrons along the conductor, opposite to the electric field, is called ________.

• velocity

• drift velocity

• Zigzag

Multiple Choice

Which is the equivalent of one electron?

• 1.6 x 10 ^-19 C

• 1.6 x 10 ^-18 C

• 1.6 x 10 ^-20 C

Multiple Choice

The SI unit of current is ______.

• Ampere

• Volts

• kilovolts

Multiple Choice

1 A (ampere) = _____

• 1Cs

• 1s/C

• 1C /s

Multiple Choice

What is producing current?

• Resistance produces current

• volts produces current

• potential difference produces current

Multiple Choice

What is the relationship between current (I) and voltage (V)?

• They are directly proportional, as current increases, voltage also increases (vice versa)

• They are indirectly proportional, as current increases, voltage also increases (vice versa)

• They are indirectly proportional; as current increases, voltage decreases

Multiple Choice

What is the relationship between current (I) and resistance (R)?

• They are directly proportional, as current increases, resistance also increases (vice versa)

• They are indirectly proportional, as current increases, resistance also increases (vice versa)

• They are indirectly proportional; as resistance, current decreases. (vice versa)

Multiple Choice

How can we generate potential difference in circuit?

• by using cell or battery

• by using insulator

• by using conductor

Multiple Choice

What is the SI unit used for resistance ?

• ohm $$\Omega$$

• Volts (V)

• Ampere (A)

Multiple Choice

It is a force that counteracts the flow of electricity.

• current

• Conductor

• Resistance

Multiple Choice

What is the formula for solving resistance ?

• $$V\ =\frac{\Delta R}{I}$$

• $$R=\frac{\Delta V}{I}$$

• $$R\ =\ \frac{I}{\Delta V}$$

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