Questions and Answers
An ampere is a unit of electrical?
Which statement is correct?
The current through a 10-ohm resistor connected to a 120-V power supply is?
A 10-ohm resistor has a 5-A current in it. What is the voltage across the resistor?
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When a 10-V battery is connected to a resistor, the current in the resistor is 2 A. What is the resistor's value?
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In a common DC circuit, electrons move at speeds of?
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When a light switch is turned on in a DC circuit, the average speed of electrons in the lamp is?
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The electric power of a lamp that carries 2 A at 120 V is?
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When two lamps are connected in parallel to a battery, the electrical resistance that the battery senses is?
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When two lamps are connected in series to a battery, the electrical resistance that the battery senses is?
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On some early automobiles, both headlights went out when one bulb burned out. The headlights must have been connected in?
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Modern automobile headlights are connected in?
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A 100-watt lamp glows brighter than a 25-watt lamp. The electrical resistance of the 100-watt lamp must be?
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In an electric circuit, the safety fuse or circuit breaker is connected to the circuit in?
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When a pair of 1-ohm resistors are connected in series, their combined resistance is?
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A circuit breaker often serves the same purpose as a?
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In a simple circuit containing a bulb, energy is given to the moving charges by?
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As more lamps are put into a series circuit, the overall current in the power source?
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As more lamps are put into a parallel circuit, the overall current in the power source?
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When we say an appliance 'uses up electricity,' we really are saying that?
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Compared to the resistance of two resistors connected in series, the same two resistors connected in parallel have?
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If you plug an electric toaster rated at 110 V into a 220-V outlet, the current in the toaster will be about?
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When a 60-watt light bulb is connected to a 120-volt source, the current in the light bulb is?
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If 0.8 A of current flow through a light bulb connected to a 120 V outlet, the power consumed is?
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The headlights, radio, and defroster fan in an automobile are connected in?
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A 4-ohm resistor is connected in parallel with a 6-ohm resistor. This combination produces an equivalent resistance of?
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The power dissipated in a 4-ohm resistor carrying 3 A is?
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Which is more dangerous, touching a faulty 110-volt light fixture, or a Van de Graaff generator charged to 100,000 volts?
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A 60-W light bulb and a 100-W light bulb are each rated at 120 V. Which light bulb has a larger resistance?
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A 60-W light bulb and a 100-W light bulb are connected in series to a 120 V outlet. Which light bulb has more current in it?
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Compared to a single lamp connected to a battery, two identical lamps connected in series to the same battery will carry?
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Compared to a single lamp connected to a battery, two lamps connected in parallel to the same battery will carry?
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An electric heater is rated at 300 W when used in a 110-V circuit. The safety fuse in the circuit can handle 15 A of current. How many heaters can be safely operated in the circuit?
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A heater uses 20 A when used in a 110-V line. If electric power costs 10 cents per kilowatt hour, the cost of running the heater for 10 hours is?
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The current through two identical light bulbs connected in series is 0.25 A. The voltage across both bulbs is 110 V. The resistance of a single light bulb is?
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A power line with a resistance of 2 ohms has a current of 80 A in it. The power dissipated in the line is?
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What is the resistance of a 120-W incandescent lamp connected to a 120-V power supply?
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Compared to the amount of electric current in the filament of a lamp, the amount of current in the connecting wire is?
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Connect a pair of lamps in series and you draw current from the connected battery. Connect the same lamps in parallel and you draw?
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Three resistors, 1-ohm, 2-ohm, and 3-ohm are connected in parallel. If they were connected in series instead, their equivalent resistance would be?
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The ratio of the potential difference across a metallic conductor to the current in the conductor is known as?
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What condition must exist between two points in a conductor in order to maintain a flow of charge?
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Study Notes
Electric Current Concepts
- An ampere (A) measures electrical current, essential in understanding circuit behavior.
- Charge flows in a closed circuit; voltage can exist in both open and closed circuits.
- To calculate current through a resistor, use Ohm's law: Current (I) = Voltage (V) / Resistance (R).
Resistor Behavior
- Voltage across a resistor can be calculated by multiplying current by resistance: ( V = I \times R ).
- A 10-V battery connected to a resistor with a 2 A current results in a resistance of 5 ohms.
Electron Movement
- In DC circuits, electron speeds measure only a fraction of a centimeter per second, irrespective of circuit layout.
- When switches in DC circuits are activated, electron speed remains low, generally under 1 cm/s.
Power and Resistance
- Electrical power (in watts) can be found using: Power (P) = Voltage (V) × Current (I).
- In parallel connections, the total resistance perceived by the battery is less than any individual lamp’s resistance.
- In series connections, the total resistance is greater than any single resistor’s resistance.
Circuit Design
- Early automobile headlights, if in series, would fail when one bulb burned out; modern designs use parallel connections to avoid this issue.
Bulb Resistance and Brightness
- A brighter 100-Watt bulb has a lower resistance than a 25-Watt bulb at the same voltage.
- A circuit breaker functions similarly to a fuse, cutting off excess current to prevent overload.
Current Flow in Circuits
- Adding lamps in a series circuit decreases overall current from the power source.
- In contrast, adding lamps in a parallel circuit increases overall current because each lamp offers a separate pathway for current.
Electrical Safety and Efficiency
- Touching a faulty 110-volt fixture tends to be more dangerous than contacting a 100,000-volt Van de Graaff generator due to current flow capacity.
- A light bulb rated at 60 watts plugged into a 120-volt outlet carries 0.5 A of current.
Resistance and Power Loss
- Power dissipated in a resistor can be calculated using: P = I² × R.
- Resistors in series add to total resistance, while resistors in parallel yield a lower combined resistance.
Cost of Electricity
- Costs for running electrical appliances can be estimated based on current draw and duration, for example, a 20 A heater on a 110 V line incurs expenses based on kilowatt-hour rates.
Summary of Resistor Configurations
- For resistors in series: Total resistance = sum of individual resistances.
- For resistors in parallel: Combined resistance formula is ( \frac{1}{R_{total}} = \sum \frac{1}{R_{individual}} ).
Conclusion of Electric Current
- The understanding of electric current, resistance, and circuit behavior is critical for applications in electronics, ensuring safety and efficiency in electrical systems.
Studying That Suits You
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Test your knowledge with these flashcards on Electric Current from Chapter 23 of your Physics course. Each card challenges you with key concepts related to electrical current, including units and circuit behavior. Perfect for quick reviews or study sessions.
