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Questions and Answers
A copper wire carries a current of 5A. If the number density of free electrons in copper is $8.5 \times 10^{28} m^{-3}$ and the cross-sectional area of the wire is $2 \times 10^{-6} m^2$, what is the drift velocity of the electrons?
A copper wire carries a current of 5A. If the number density of free electrons in copper is $8.5 \times 10^{28} m^{-3}$ and the cross-sectional area of the wire is $2 \times 10^{-6} m^2$, what is the drift velocity of the electrons?
- $9.20 \times 10^{-5} m/s$
- $4.60 \times 10^{-5} m/s$
- $3.68 \times 10^{-4} m/s$
- $1.84 \times 10^{-4} m/s$ (correct)
A heating element in an electric kettle has a resistance of 20Ω. If the kettle is connected to a 240V supply, how much electrical energy is converted into heat in 5 minutes?
A heating element in an electric kettle has a resistance of 20Ω. If the kettle is connected to a 240V supply, how much electrical energy is converted into heat in 5 minutes?
- 288 kJ
- 1728 kJ
- 576 kJ
- 864 kJ (correct)
A battery with an EMF of 12V has an internal resistance of 0.5Ω. If the battery is connected to a 3.5Ω resistor, what is the terminal voltage of the battery?
A battery with an EMF of 12V has an internal resistance of 0.5Ω. If the battery is connected to a 3.5Ω resistor, what is the terminal voltage of the battery?
- 10.5 V (correct)
- 1.5 V
- 3.0 V
- 12 V
Two resistors, 4Ω and 6Ω, are connected in parallel. What is the equivalent resistance of the parallel combination?
Two resistors, 4Ω and 6Ω, are connected in parallel. What is the equivalent resistance of the parallel combination?
A wire has a resistance of 10Ω at 20°C. If the temperature coefficient of resistance for the material of the wire is $0.004 °C^{-1}$, what is the resistance of the wire at 70°C?
A wire has a resistance of 10Ω at 20°C. If the temperature coefficient of resistance for the material of the wire is $0.004 °C^{-1}$, what is the resistance of the wire at 70°C?
If the potential difference across a resistor is doubled, how does the power dissipated by the resistor change, assuming the resistance remains constant?
If the potential difference across a resistor is doubled, how does the power dissipated by the resistor change, assuming the resistance remains constant?
Which of the following changes will increase the resistance of a metallic conductor?
Which of the following changes will increase the resistance of a metallic conductor?
A parallel plate capacitor is charged by a battery. If a dielectric material is inserted between the plates while the battery remains connected, what happens to the charge on the capacitor?
A parallel plate capacitor is charged by a battery. If a dielectric material is inserted between the plates while the battery remains connected, what happens to the charge on the capacitor?
Three resistors, 2Ω, 4Ω, and 6Ω, are connected in series to a 12V battery. What is the current flowing through the 2Ω resistor?
Three resistors, 2Ω, 4Ω, and 6Ω, are connected in series to a 12V battery. What is the current flowing through the 2Ω resistor?
A device operating at 120V draws a current of 2A. If the cost of electricity is $0.10 per kilowatt-hour, how much does it cost to operate the device for 30 minutes?
A device operating at 120V draws a current of 2A. If the cost of electricity is $0.10 per kilowatt-hour, how much does it cost to operate the device for 30 minutes?
What happens to the drift velocity of electrons in a conductor if both the voltage across the conductor and the length of the conductor are doubled, assuming all other factors remain constant?
What happens to the drift velocity of electrons in a conductor if both the voltage across the conductor and the length of the conductor are doubled, assuming all other factors remain constant?
For a non-ohmic material, which of the following statements is true?
For a non-ohmic material, which of the following statements is true?
A light bulb is rated at 60W when operated at 120V. What is the resistance of the light bulb?
A light bulb is rated at 60W when operated at 120V. What is the resistance of the light bulb?
Two wires are made of the same material. Wire A has length L and diameter d, while wire B has length 2L and diameter 2d. What is the ratio of the resistance of wire A to the resistance of wire B?
Two wires are made of the same material. Wire A has length L and diameter d, while wire B has length 2L and diameter 2d. What is the ratio of the resistance of wire A to the resistance of wire B?
A battery has an EMF of 15V and an internal resistance of 1Ω. What is the maximum current that can be drawn from the battery?
A battery has an EMF of 15V and an internal resistance of 1Ω. What is the maximum current that can be drawn from the battery?
Which of the following factors does NOT affect the resistivity of a material?
Which of the following factors does NOT affect the resistivity of a material?
If the area of a conductor is doubled and the voltage remains constant, what happens to the current through it?
If the area of a conductor is doubled and the voltage remains constant, what happens to the current through it?
A 100 W light bulb is connected to a 200 V power supply. If the voltage drops to 180 V, what will be the power consumed by the bulb, assuming its resistance remains constant?
A 100 W light bulb is connected to a 200 V power supply. If the voltage drops to 180 V, what will be the power consumed by the bulb, assuming its resistance remains constant?
In a series circuit consisting of two resistors, $R_1$ and $R_2$ where $R_1 > R_2$, which resistor dissipates more power?
In a series circuit consisting of two resistors, $R_1$ and $R_2$ where $R_1 > R_2$, which resistor dissipates more power?
Two identical resistors are connected in parallel to a voltage source. If one of the resistors is removed from the circuit, what happens to the total current supplied by the source?
Two identical resistors are connected in parallel to a voltage source. If one of the resistors is removed from the circuit, what happens to the total current supplied by the source?
Flashcards
Current Electricity
Current Electricity
The flow of electric charge through a conductor.
Electric Current (I)
Electric Current (I)
The rate of flow of electric charge (Q) through a cross-sectional area in a conductor; measured in Amperes (A).
Drift Velocity (vd)
Drift Velocity (vd)
The average velocity attained by charged particles in a material due to an electric field.
Potential Difference (V)
Potential Difference (V)
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Resistance (R)
Resistance (R)
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Resistivity (ρ)
Resistivity (ρ)
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Ohm's Law
Ohm's Law
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Electrical Power (P)
Electrical Power (P)
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Series Circuits
Series Circuits
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Parallel Circuits
Parallel Circuits
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Joule Heating
Joule Heating
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Electromotive Force (EMF)
Electromotive Force (EMF)
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Internal Resistance (r)
Internal Resistance (r)
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Study Notes
- Current electricity is the flow of electric charge through a conductor.
- Electric charge is carried by moving electrons or ions.
- Current is measured in Amperes (A).
Electric Current
- Electric current (I) is defined as the rate of flow of electric charge (Q) through a cross-sectional area in a conductor.
- I = Q/t, where I is current, Q is charge, and t is time.
- The direction of conventional current is taken as the direction of positive charge flow, opposite to the direction of electron flow.
- 1 Ampere (1A) is equal to 1 Coulomb per second (1 C/s).
Drift Velocity
- Drift velocity (vd) is the average velocity attained by charged particles in a material due to an electric field.
- In a conductor, electrons move randomly but drift slowly in a specific direction when an electric field is applied.
- Drift velocity is proportional to the electric field and inversely proportional to the number density of free electrons.
- I = nAvd e, where n is the number density of electrons, A is the cross-sectional area, vd is the drift velocity, and e is the elementary charge.
Potential Difference
- Potential difference (V) is the difference in electric potential between two points in a circuit.
- It is measured in Volts (V).
- Voltage is the energy required to move a unit charge between two points.
- V = W/Q, where V is potential difference, W is work done (energy), and Q is charge.
Resistance
- Resistance (R) is the opposition to the flow of electric current in a material.
- It is measured in Ohms (Ω).
- Resistance depends on the material's properties, length, and cross-sectional area.
- R = ρL/A, where ρ is resistivity, L is length, and A is the cross-sectional area.
- Resistivity (ρ) is a material's intrinsic ability to resist current flow. Its unit is Ohm-meter (Ω⋅m).
Ohm's Law
- Ohm's Law states that the potential difference (V) across a conductor is directly proportional to the current (I) flowing through it, provided the temperature and other physical conditions remain constant.
- V = IR, where V is voltage, I is current, and R is resistance.
- Ohm's Law is applicable to many materials but not all (non-ohmic materials).
Temperature Dependence of Resistance
- The resistance of most materials changes with temperature.
- For most metals, resistance increases with increasing temperature.
- R = R0[1 + α(T - T0)], where R is resistance at temperature T, R0 is resistance at reference temperature T0, and α is the temperature coefficient of resistance.
- Semiconductors typically exhibit a decrease in resistance with increasing temperature due to increased carrier concentration.
Electrical Power
- Electrical power (P) is the rate at which electrical energy is converted into another form of energy (e.g., heat, light).
- P = VI, where P is power, V is voltage, and I is current.
- Using Ohm's Law, power can also be expressed as P = I^2R or P = V^2/R.
- Power is measured in Watts (W).
Series Circuits
- In a series circuit, components are connected end-to-end, so the same current flows through each component.
- The total resistance in a series circuit is the sum of the individual resistances: R_total = R1 + R2 + R3 + ...
- The voltage across each component in a series circuit may be different, but the sum of the voltages across each component equals the total voltage supplied by the source.
- V_total = V1 + V2 + V3 + ...
Parallel Circuits
- In a parallel circuit, components are connected side-by-side, so the voltage across each component is the same.
- The reciprocal of the total resistance in a parallel circuit is the sum of the reciprocals of the individual resistances: 1/R_total = 1/R1 + 1/R2 + 1/R3 + ...
- The total current in a parallel circuit is the sum of the currents through each branch: I_total = I1 + I2 + I3 + ...
Electrical Energy and Joule Heating
- Electrical energy (E) is the energy supplied by an electrical circuit.
- E = Pt, where E is energy, P is power, and t is time.
- Energy is measured in Joules (J).
- Joule heating (also known as resistive heating or ohmic heating) is the process by which the passage of an electric current through a conductor releases heat.
- The heat generated (H) is given by H = I^2Rt, where I is current, R is resistance, and t is time.
Electromotive Force (EMF)
- Electromotive force (EMF) is the voltage provided by a source of electrical energy, such as a battery or generator.
- It is the potential difference across the terminals of the source when no current is flowing.
- EMF is measured in Volts (V).
Internal Resistance
- Internal resistance (r) is the resistance within a voltage source (e.g., battery) that causes a drop in voltage when current flows.
- The terminal voltage (V) of a battery is related to its EMF (ε) and internal resistance (r) by V = ε - Ir, where I is the current flowing through the battery.
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