2C2 Electricity and Magnetism Flashcards
Describe how principles electricity and magnetism explain electric charge, circuits, and magnetic fields.
What is electricity?
The presence and flow of electric charge.
It is usually carried by electrons moving through a conductor.
What is electric charge?
A property that determines how matter interacts with electric and magnetic fields.
Charge exists in two forms: positive and negative. Objects with the same charge repel each other, while opposite charges attract.
True or False:
Like charges attract each other.
False
Like charges repel each other, while opposite charges attract.
What is the unit of electric charge?
Coulomb
(C)
One Coulomb is approximately equal to 6.242 × 10¹⁸ elementary charges.
What does Coulomb’s law describe?
The force between two charges.
It states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
What is the formula for Coulomb’s law?
F = k × (q₁ × q₂) / r²
Where:
F is the electrostatic force between the charges,
k is Coulomb’s constant,
q₁ and q₂ are the charges, and
r is the distance between them.
Fill in the blank:
Opposite charges _______ each other.
attract
Opposite charges create an attractive force, as described by Coulomb’s law.
What happens when charges are separated by a greater distance?
The force between them decreases.
According to Coulomb’s law, the force is inversely proportional to the square of the distance between the charges.
Fill in the blank:
Coulomb’s constant, k, is approximately _______ N·m²/C².
8.99 × 10⁹
Coulomb’s constant is used to calculate the electrostatic force between two charges.
What is an electric field?
A region around a charge where other charges experience a force.
The strength depends on the magnitude of the charge and the distance from it.
True or False:
The electric field strength increases with distance from the charge.
False
The electric field strength decreases with the square of the distance from the charge.
How is the strength of an electric field calculated?
E = F / q
Where E is the electric field, F is the force, and q is the charge.
True or False:
The electric field lines point toward negative charges.
True
The field lines always point from positive to negative charges, indicating the direction of the force that would be exerted on a positive test charge.
What is the unit of electric field strength?
N/C
(Newtons per Coulomb)
The unit describes the force exerted on a charge in an electric field.
True or False:
The electric field strength is stronger the farther you are from the charge.
False
The electric field strength decreases with the square of the distance from the charge.
What determines the direction of an electric field?
The sign of the charge.
Electric fields point away from positive charges and toward negative charges.
What type of force does an electric field exert on a charge?
Attractive or repulsive force.
Positive charges are repelled by other positive charges and attracted to negative charges, and vice versa.
What happens to the force between two charges when the distance is halved?
It quadruples.
According to Coulomb’s law, force is inversely proportional to the square of the distance, so halving the distance increases the force by a factor of four.
True or False:
Electric fields can only exist around charged objects.
True
They are created by charges, and their presence can be detected by observing forces on other charges.
What is a conductor?
A material that allows electric charge to flow easily.
Metals like copper and silver are good conductors due to the availability of free electrons.
What is an insulator?
A material that resists the flow of electric charge.
Insulating materials, like rubber and glass, have tightly bound electrons that do not move freely.
True or False:
Metals are good conductors of electricity.
True
Metals, especially copper and silver, have free electrons that allow them to conduct electricity efficiently.
Fill in the blank:
Rubber is an example of a good _______.
insulator
Rubber is often used in electrical wires to prevent accidental electrical contact.
What is the function of an insulator in electrical wiring?
To prevent the unwanted flow of electric charge.
Insulators are used to cover wires, ensuring that the current only flows through the designated path.
What is the electric field inside a conductor?
Zero
In a conductor in electrostatic equilibrium, charges move to the surface, and the electric field inside cancels out.
True or False:
In conductors, free electrons move towards the positive end when a voltage is applied.
True
Free electrons in conductors move toward the positive terminal, creating an electric current.
What is electric current?
The flow of electric charge.
Current is carried by electrons in a conductor.
What is the unit of electric current?
Ampere
(A)
One ampere is equal to one coulomb of charge passing through a conductor per second.
Fill in the blank:
________ is the opposition to the flow of electric current.
Resistance
Resistance depends on the material, length, and cross-sectional area of the conductor.
True or False:
An Ohm (Ω) is the unit of resistance.
True
One ohm is the resistance that allows one ampere of current to flow when one volt is applied across the conductor.
What is voltage?
The difference in electric potential between two points.
Voltage is responsible for driving the current through a conductor and is measured in volts (V).
What is the unit of voltage?
Volt
(V)
One volt is the potential difference that will move one coulomb of charge when one joule of work is done.
What is Ohm’s law?
The relationship between voltage, current, and resistance.
Ohm’s law is expressed as: V = I × R, where V is voltage (volts), I is current (amperes), and R is resistance (ohms).
True or False:
Power in an electrical circuit is calculated by multiplying voltage by current.
True
Power is given by P = V × I, where P is power (watts), V is voltage (volts), and I is current (amperes).
What is the formula for Ohm’s Law?
V=IR
Where voltage (V) = current (I) multiplied by resistance (R).
What is the unit of electrical power?
Watt
(W)
One watt is equivalent to one joule of energy used per second.
True or False:
Power is the same as energy.
False
Power is the rate at which energy is used, while energy is the total work done over time.
Define:
Direct current
(DC)
Electric current that flows in one direction.
DC is commonly used in batteries, where electrons flow from the negative to the positive terminal.
What is alternating current?
(AC)
Electric current that changes direction.
AC is used in most household electrical systems, with current oscillating back and forth.
Fill in the blank:
The formula for resistance is R = V / I, where V is the _______ and I is the current.
voltage
This formula is derived from Ohm’s law and shows how resistance relates to voltage and current.
What is capacitance?
The ability of a component to store an electric charge.
Capacitance is measured in farads (F), and capacitors are used to store and release electrical energy. It is calculated by dividing the charge stored on the capaictor by the voltage.
What is the unit of capacitance?
Farad
(F)
One farad is the capacitance of a capacitor that stores one coulomb of charge when one volt is applied.
True or False
A capacitor is a device used to store electrical energy.
True
Capacitors store charge between two conductors separated by a dielectric material.
What is a battery?
A device that converts chemical energy into DC power.
Batteries convert chemical energy into electrical energy and are commonly used in portable devices.
What is a generator?
A device that converts mechanical energy into electrical energy.
Generators produce alternating current (AC) by rotating a coil within a magnetic field.
What is the function of a photocell?
To convert light energy into electrical energy.
Photocells, or solar cells, are used in devices like solar panels to generate electricity from sunlight.
What is a series circuit?
A circuit where components are connected end to end.
The current is the same through all components, but the voltage is divided among them.
What happens to the total resistance in a series circuit?
It increases.
The a series circuit, the total resistance is the sum of the individual resistances: R_total = R₁ + R₂ + …
What is a parallel circuit?
A circuit where components are connected across common points.
The voltage across all components is the same, but the current is divided among them.
Fill in the blank:
In a parallel circuit, the total resistance ________.
decreases
The total resistance is calculated using: 1/Rₜₒₜₐₗ = 1/R₁ + 1/R₂ + …, where R₁ and R₂ represent the resistance of each individual circuit.
True or False:
In a parallel circuit, the current is the same through all components.
False
The voltage is the same, but the current divides according to the resistance of each branch.
What is the equivalent resistance of two resistors in parallel?
Rtotal = R₁ + R₂ / R₁ × R₂
This formula is used for two resistors in parallel to find the total resistance of the circuit.
What happens if more resistors are added in parallel?
The total resistance decreases.
Adding resistors in parallel provides more paths for the current, reducing the overall resistance.
What happens to the current if more resistors are added in series?
It decreases.
Adding resistors increases the total resistance, which reduces the overall current according to Ohm’s law.
What does a fuse do in a circuit?
It protects the circuit from excessive current.
A fuse melts if the current exceeds a certain limit, preventing damage to the components.
True or False:
The voltage across all components in a series circuit is the same.
False
In a series circuit, the voltage is divided among the components according to their resistances.
True or False:
The total resistance in a parallel circuit is greater than the resistance of the smallest resistor.
False
The total resistance in a parallel circuit is always less than the resistance of the smallest individual resistor.
Define:
magnetic forces
A force that results from the attraction or repulsion between electrically charged particles in motion.
What are the two types of magnetic poles?
North and South
Opposite poles attract each other, while like poles repel.
Fill in the blank:
The region around a magnet where magnetic forces are exerted is called a/an _______ _____.
magnetic field
They are represented by field lines that emerge from the north pole and enter the south pole.
True or False:
Magnetic poles can exist independently.
False
Magnetic poles always come in pairs; cutting a magnet results in two smaller magnets, each with a north and south pole.
What happens when you bring the north pole of one magnet close to the north pole of another magnet?
They repel each other.
This demonstrates the principle that like poles repel.
What shape do magnetic field lines around a bar magnet take?
Closed loops
These lines emerge from the north pole, curve around, and re-enter at the south pole.
What is a permanent magnet?
A magnet that remains magnetized without external power.
Examples include bar magnets and horseshoe magnets.
What is an electromagnet?
A magnet formed by electric current through a coil.
Electromagnets can be turned on or off by controlling the electric current.
True or False:
Electromagnets are weaker than permanent magnets.
False
Electromagnets can be made much stronger by increasing the current or the number of coils.
Fill in the blank:
The core of an electromagnet is typically made of _______.
iron
Iron enhances the magnetic field produced by the current in the coil.
What advantage do electromagnets have over permanent magnets?
Their magnetic field can be controlled
They can be turned on and off, as well as adjusted, making them useful in devices such as electric motors and relays.
How is the direction of the magnetic field around a current-carrying wire determined?
By using the right-hand rule.
Point your thumb in the direction of current flow; your curled fingers show the direction of the magnetic field.
True or False:
A straight current-carrying wire produces a circular magnetic field.
True
The magnetic field forms concentric circles around the wire.
Fill in the blank:
The strength of the magnetic field around a current-carrying wire is _______ proportional to the distance from the wire.
inversely
This means the field gets weaker as you move farther away.
What is electromagnetic induction?
The process of generating an electric current by changing a magnetic field.
This principle was discovered by Michael Faraday.
True or False:
A stationary magnet near a stationary coil will generate an electric current.
False
A changing magnetic field is necessary to induce a current.
Fill in the blank:
The device used to demonstrate electromagnetic induction is called a/an _______.
generator
Generators convert mechanical energy into electrical energy.
What law quantitatively describes electromagnetic induction?
Faraday’s Law of Induction
The law states that the induced voltage is proportional to the rate of change of the magnetic flux.
What is the basic function of an electric motor?
To convert electrical energy into mechanical energy.
This is achieved through the interaction of magnetic fields and current-carrying wires.
What is the basic function of an electric generator?
To convert mechanical energy into electrical energy.
This process relies on electromagnetic induction.
True or False:
Both motors and generators rely on magnetic fields.
True
Magnetic fields are essential for the operation of both devices.
Fill in the blank:
The rotation of a coil in a magnetic field generates a _______.
current
This is the principle behind how generators work.
What component of a motor ensures continuous rotation in the same direction?
The commutator.
The commutator reverses the current direction in the coil, maintaining consistent torque.
What is the role of the armature in a motor?
To carry the current and rotate within the magnetic field.
The armature is the moving part of a DC motor.
What is the function of a stator in a motor?
To provide a stationary magnetic field.
The rotor moves within this field to create motion.
Fill in the blank:
A generator’s rotor _______ to induce current in the stator.
rotates
The rotor is the moving part in an AC motor, while the stator remains stationary.
