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Questions and Answers
What does Ohm's Law describe?
What does Ohm's Law describe?
- The direct proportionality of current density to electric field for certain materials. (correct)
- The behavior of all materials under electrical conditions.
- The relationship between voltage and resistance only.
- The inverse relationship between current density and electric field.
Which factor primarily affects the resistivity of a conductor?
Which factor primarily affects the resistivity of a conductor?
- The material of the conductor. (correct)
- The length of the conductor.
- The voltage applied across the conductor.
- The cross-sectional area of the conductor.
If the temperature of a conductor increases, what happens to its resistivity?
If the temperature of a conductor increases, what happens to its resistivity?
- It increases. (correct)
- It becomes zero.
- It decreases.
- It remains constant.
What is the relationship between resistance and resistivity if resistivity is constant?
What is the relationship between resistance and resistivity if resistivity is constant?
What happens to current density in a semiconductor if the electric field is maintained while lowering its temperature?
What happens to current density in a semiconductor if the electric field is maintained while lowering its temperature?
What is the SI unit for resistivity?
What is the SI unit for resistivity?
When is a material considered ohmic?
When is a material considered ohmic?
What is the effect of a material's temperature coefficient of resistivity on its resistivity?
What is the effect of a material's temperature coefficient of resistivity on its resistivity?
What is the relationship between resistance and temperature described in the equation 𝑅(𝑇) = 𝑅0[1 + 𝛼(𝑇 − 𝑇0)]?
What is the relationship between resistance and temperature described in the equation 𝑅(𝑇) = 𝑅0[1 + 𝛼(𝑇 − 𝑇0)]?
How is the resistivity of a wire calculated from its resistance?
How is the resistivity of a wire calculated from its resistance?
If the voltage across a copper wire is doubled, how is the current affected?
If the voltage across a copper wire is doubled, how is the current affected?
What is the primary factor that prevents the escape of electrons from a conductor without an internal electric field?
What is the primary factor that prevents the escape of electrons from a conductor without an internal electric field?
What does electromotive force (EMF) represent in a circuit?
What does electromotive force (EMF) represent in a circuit?
Which statement correctly describes the purpose of a resistor in a circuit?
Which statement correctly describes the purpose of a resistor in a circuit?
What is the drift velocity of electrons in copper as stated?
What is the drift velocity of electrons in copper as stated?
How does current density (J) relate to the drift velocity (vd)?
How does current density (J) relate to the drift velocity (vd)?
Which factor affects the resistance of a wire?
Which factor affects the resistance of a wire?
Why is it important to distinguish that electromotive force is not a force?
Why is it important to distinguish that electromotive force is not a force?
What unit is equivalent to 1 C/s?
What unit is equivalent to 1 C/s?
What happens to the potential energy in a conductor during a complete circuit?
What happens to the potential energy in a conductor during a complete circuit?
In a current-carrying wire, how is current defined?
In a current-carrying wire, how is current defined?
What is the expression for calculating the current (I) in a conductor?
What is the expression for calculating the current (I) in a conductor?
What does a positive internal electric field in a conductor do to free electrons?
What does a positive internal electric field in a conductor do to free electrons?
If a copper wire has a cross-sectional area of $2.05 \times 10^{-3} m^2$ and carries a current of 4.85 A, what is the current density?
If a copper wire has a cross-sectional area of $2.05 \times 10^{-3} m^2$ and carries a current of 4.85 A, what is the current density?
What is the formula used to calculate electric power in relation to resistance?
What is the formula used to calculate electric power in relation to resistance?
In calculating the electric field across a cylindrical cable, what is the derived value when using a 220-V potential difference?
In calculating the electric field across a cylindrical cable, what is the derived value when using a 220-V potential difference?
What is the required diameter of a cylindrical copper cable to produce heat at 75.0 W?
What is the required diameter of a cylindrical copper cable to produce heat at 75.0 W?
What is the relationship between the resistivity, length, and diameter of a cylindrical conductor when determining its resistance?
What is the relationship between the resistivity, length, and diameter of a cylindrical conductor when determining its resistance?
If a cylindrical cable has a length of 1500 m and is defined by a specific resistivity, what variable does not affect the production of heat in this context?
If a cylindrical cable has a length of 1500 m and is defined by a specific resistivity, what variable does not affect the production of heat in this context?
What is the relationship between terminal voltage and electromotive force for a real EMF source?
What is the relationship between terminal voltage and electromotive force for a real EMF source?
If a 5.0 V battery with an internal resistance of 0.5 Ω is connected to a 2.0-Ω resistor, what current flows through the resistor?
If a 5.0 V battery with an internal resistance of 0.5 Ω is connected to a 2.0-Ω resistor, what current flows through the resistor?
What happens to the reading on an ideal voltmeter connected in a circuit with an open circuit condition?
What happens to the reading on an ideal voltmeter connected in a circuit with an open circuit condition?
For a battery with an emf of 12.0 V and an internal resistance of 0.40 Ω, what resistance will yield a power dissipation of 80.0 W?
For a battery with an emf of 12.0 V and an internal resistance of 0.40 Ω, what resistance will yield a power dissipation of 80.0 W?
How is power dissipated in a resistor expressed in terms of voltage and current?
How is power dissipated in a resistor expressed in terms of voltage and current?
In a closed circuit with both EMF and internal resistance, what is the expected voltage drop across the internal resistance?
In a closed circuit with both EMF and internal resistance, what is the expected voltage drop across the internal resistance?
If the internal resistance is increased in a circuit with constant EMF, what happens to the terminal voltage?
If the internal resistance is increased in a circuit with constant EMF, what happens to the terminal voltage?
What is a characteristic of an ideal voltmeter in a circuit?
What is a characteristic of an ideal voltmeter in a circuit?
Study Notes
Current
- Current is the motion of charge from one region to another.
- For a conductor with no internal electric field, there is no net flow of charge, resulting in no current.
- For a conductor with an internal electric field, free electrons accelerate in the direction of the force, but collisions with ions cause them to change direction. This slow, net motion is called drift motion.
- Current is not a vector quantity. It is always along the length of the wire, even when curved.
Current Density
- Current density (J) is the current per unit cross-sectional area.
- It is calculated as: J = I/A = nqvd, where vd is the drift velocity, q is the magnitude of the charge, and n is the concentration of particles.
- The SI unit of current density is 1 C/s∙m2 or 1 A/m2.
Ohm's Law
- Ohm's Law states that current density is directly proportional to the electric field.
- The ratio of electric field to current density is constant and is called resistivity (ρ).
- Ohm's Law is an idealized model that describes the behavior of some materials well but is not universally applicable.
- Materials that obey Ohm's Law are called ohmic or linear conductors.
Resistivity
- Resistivity is the ratio of the magnitudes of electric field and current density: ρ = E/J.
- It is a measure of a material's resistance to the flow of current. Good conductors have low resistivity, while good insulators have high resistivity.
- Resistivity depends on the type of material and temperature.
- The SI unit of resistivity is 1 Ω∙m.
Conductivity
- Conductivity is the reciprocal of resistivity.
- It is a measure of a material's ability to conduct electricity.
- The SI unit of conductivity is 1/ Ω∙m.
Resistance
- Resistance (R) is the relationship between resistivity, length, and cross-sectional area of a conductor: R = ρL/A.
- Resistance is also related to voltage (V) and current (I): R = V/I.
- This relationship is another way to express Ohm's Law.
- The SI unit of resistance is 1 Ohm (Ω).
Electromotive Force (EMF)
- EMF is the energy per unit charge that a device provides to a circuit.
- Examples of EMF sources include batteries, generators, solar cells, thermocouples, and fuel cells.
- EMF is not a force but a potential difference.
- The terminal voltage (Vab) of a real EMF source is less than its EMF due to internal resistance (r): Vab = ξ - Ir.
Energy and Power in Circuits
- Power (P) is the rate at which energy is delivered to or extracted from a circuit element: P = VabI.
- The SI unit of power is 1 Watt (W).
- Power dissipated in a resistor: P = VabI = I2R = Vab2/R.
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Description
Explore the concepts of electric current, current density, and Ohm's Law in this quiz. Understand how charge flows in conductors, the relationship between current density and electric field, and the underlying principles governing these phenomena. Test your knowledge with practical examples and calculations.
