Chapter 23: Electric Current

The current through a resistor can be calculated using Ohm's Law, which states that current (I) is equal to voltage (V) divided by resistance (R). In this case, the voltage is given as 120 V and the resistance is 10 ohms. Therefore, the current is calculated as 120 V / 10 ohms = 12 A.

The power consumed by an electrical device can be calculated using the formula P = IV, where P is power, I is current, and V is voltage. In this case, the current is given as 0.8 A and the voltage is 120 V. Plugging these values into the formula, we get P = 0.8 A * 120 V = 96 W. Therefore, the correct answer is 96 W.

Automobile headlights are connected in parallel because they are designed to operate independently of each other. When headlights are connected in parallel, each headlight has its own separate circuit and power source. This means that if one headlight were to malfunction or burn out, the other headlight would still continue to function properly. Additionally, connecting headlights in parallel allows for equal voltage distribution, ensuring that both headlights receive the same amount of power and brightness.

An ampere is a unit of electrical current. It measures the rate at which electric charge flows in a circuit. It is commonly used to quantify the amount of current flowing through a conductor. The other options, such as electrical pressure and resistance, are not correct because they do not accurately describe what an ampere measures. Therefore, the correct answer is current.

When two lamps are connected in series to a battery, the electrical resistance that the battery senses is more than the resistance of either lamp. This is because in a series circuit, the total resistance is equal to the sum of the individual resistances. Therefore, when the two lamps are connected in series, their resistances add up, resulting in a higher total resistance that the battery senses.

A capacitor is an electronic component that stores electrical energy in an electric field. When a voltage is applied across the capacitor, it accumulates charge on its plates, thus storing both charge and energy. The charge is stored in the form of electrons on the capacitor plates, while the energy is stored in the electric field between the plates. Therefore, the correct answer is that a capacitor is used to store both charge and energy.

According to Ohm's Law, the voltage across a resistor is equal to the current flowing through it multiplied by the resistance. In this case, the current is 5 A and the resistance is 10 ohms. Therefore, the voltage across the resistor is 5 A * 10 ohms = 50 V. Since 50 V is more than 20 V, the answer is "more than 20 V".

Electrons move in an electrical circuit by interacting with an established electric field. When a voltage is applied to a circuit, an electric field is created, which exerts a force on the electrons. This force causes the electrons to move through the circuit, from the negative terminal to the positive terminal. The electrons do not move by being bumped by other electrons or by colliding with molecules, as these interactions do not provide a consistent and directed motion. The thickness of the wires does not play a significant role in the movement of electrons in a circuit.

A wire that carries an electric current may be electrically charged because the flow of electric charges through the wire creates an electric field around it. This electric field can cause the wire to become charged, depending on the conditions and materials involved. Therefore, it is possible for a wire carrying an electric current to be electrically charged.

When a woman experiences an electrical shock, the electrons that cause the shock come from her own body. This is because our bodies can store and conduct electricity. When there is a difference in electrical potential between two parts of the body or between the body and an external object, electrons can flow through the body, resulting in an electrical shock.

The current in a resistor is determined by Ohm's Law, which states that the current (I) flowing through a resistor is equal to the voltage (V) across the resistor divided by the resistance (R) of the resistor. In this case, we are given that the current is 2 A and the voltage is 10 V. By rearranging Ohm's Law to solve for resistance, we can calculate the resistor's value. The formula is R = V/I, so the resistor's value is 10 V / 2 A = 5 ohms.

The electric power of a lamp can be calculated using the formula P = IV, where P is the power, I is the current, and V is the voltage. In this case, the lamp carries 2 A at 120 V. Plugging these values into the formula, we get P = 2 A * 120 V = 240 watts. Therefore, the correct answer is 240 watts.

An electrical diode is a device that allows current to flow in only one direction. It acts as a rectifier, converting alternating current (AC) to direct current (DC). This is achieved by allowing the positive half-cycles of the AC signal to pass through while blocking the negative half-cycles. Therefore, the diode is useful for changing AC to DC, making it the correct answer.

When lamps are connected in parallel, each lamp has its own separate path for current to flow. This means that as more lamps are added, more paths are created for the current to pass through. As a result, the overall current in the power source increases because the total resistance of the circuit decreases.

When a coulomb of charge passes through a 6-volt battery, it gains 6 joules of energy. This is because the energy gained by a charge is equal to the product of the voltage and the charge. In this case, the voltage is 6 volts, and the charge is 1 coulomb. Therefore, the energy gained is 6 joules.

A circuit breaker often serves the same purpose as a fuse. A fuse is a safety device that protects electrical circuits from excessive current by melting and breaking the circuit when there is a fault. Similarly, a circuit breaker automatically interrupts the flow of electricity when it detects an overload or short circuit, thereby protecting the circuit from damage. Both the fuse and circuit breaker have the same function of preventing electrical fires and protecting electrical equipment.

In a simple circuit containing a bulb, energy is given to the moving charges by a generator. This is because a generator converts mechanical energy into electrical energy, which is then supplied to the bulb. The bulb acts as a load and converts the electrical energy into light and heat. The wires in the circuit simply serve as conduits for the flow of electrical current.

When a copper wire is stretched and made thinner, its cross-sectional area decreases. Resistance is directly proportional to the length of the wire and inversely proportional to its cross-sectional area. Therefore, when the cross-sectional area decreases, the resistance increases.

When resistors are connected in parallel, the equivalent resistance is calculated using the formula 1/Req = 1/R1 + 1/R2 + 1/R3 + ... In this case, the formula becomes 1/Req = 1/4 + 1/6. Solving this equation gives the value of Req as 2.4 ohms, which is the equivalent resistance of the combination.

When two lamps are connected in parallel to the same battery, each lamp forms a separate pathway for the flow of current. This means that the current is divided between the two lamps, resulting in each lamp carrying a portion of the total current. Therefore, compared to a single lamp connected to the battery, two lamps connected in parallel will carry more current.

The current in a circuit can be calculated using Ohm's Law, which states that current (I) is equal to voltage (V) divided by resistance (R). In this case, the resistance of the light bulb is not given, but we can assume it is constant. Therefore, when the voltage is doubled from 120 volts to 240 volts, the current is halved. Since the current is halved, it would be 0.5 A when the light bulb is connected to a 120-volt source.

The explanation for the correct answer, zero, is that the question is referring to the number of electrons delivered to an average American home. While power utilities do deliver electricity to homes, it is important to understand that electricity is the flow of electrons through a circuit. The number of electrons delivered is not a relevant measure of the amount of electricity consumed by a home. Therefore, the correct answer is zero, as the question is asking for the number of electrons delivered, which is not a meaningful quantity to measure in this context.

In an automobile, the headlights, radio, and defroster fan are connected in parallel with a switch for each. This means that each component has its own switch, allowing them to be operated independently. In a parallel circuit, the components are connected in such a way that the current has multiple paths to flow through. Therefore, turning on or off one component does not affect the others. This arrangement allows the driver to control each component individually without interfering with the functioning of the others.

The power dissipated in a resistor can be calculated using the formula P = I^2 * R, where P is power, I is current, and R is resistance. In this case, the resistance is given as 4 ohms and the current is given as 3 A. Plugging these values into the formula, we get P = 3^2 * 4 = 9 * 4 = 36 W. Therefore, the power dissipated in the resistor is 36 W.

To calculate the cost of running the heater for 10 hours, we need to find the total energy consumed by the heater in kilowatt-hours (kWh) and then multiply it by the cost per kilowatt-hour.

The power consumed by the heater can be calculated using the formula: P = VI, where P is the power in watts, V is the voltage in volts, and I is the current in amperes.

Given that the heater uses 20 A and operates on a 110-V line, the power consumed is 20 A * 110 V = 2200 W or 2.2 kW.

Now, to find the energy consumed in 10 hours, we multiply the power by the time: 2.2 kW * 10 hours = 22 kWh.

Finally, multiplying the energy consumed by the cost per kilowatt-hour (10 cents or $0.10), we get the cost of running the heater for 10 hours as $0.10/kWh * 22 kWh = $2.20.

In a common dc circuit, electrons move at speeds of a fraction of a centimeter per second. This is because in a dc circuit, the flow of electrons is relatively slow compared to the speed of light or sound waves. The movement of electrons is hindered by the resistance of the circuit components, which slows down their speed. Therefore, the speed at which electrons move in a dc circuit is only a fraction of a centimeter per second.

When there is a potential difference across the ends of a wire, it creates an electric field that exerts a force on the electrons in the wire. This force causes the electrons to move and flow in the wire, creating an electric current. Therefore, the presence of a potential difference across the ends of the wire is what causes electrons to flow, rather than an imbalance of charges or more potential energy at one end.

When a copper wire is heated, its electric resistance increases. This is because as the temperature of the wire increases, the atoms in the wire vibrate more vigorously, which leads to more collisions between the electrons and the atoms. These collisions impede the flow of electrons, causing an increase in resistance. Therefore, heating a copper wire results in an increase in its electric resistance.

Alternating current is normally produced by a generator. A battery is not capable of producing alternating current as it provides direct current. On the other hand, a generator converts mechanical energy into electrical energy, producing alternating current. Therefore, a generator is the correct answer for the given question.

When lamps are connected in series, the total voltage of the battery is divided among the lamps. The voltage across each lamp is directly proportional to its resistance. Since the lamps are made of the same material, the lamp with the thicker filament will have a lower resistance compared to the lamp with the thinner filament. According to Ohm's law (V = IR), a lower resistance will result in a higher voltage across the lamp. Therefore, the voltage is greater across the lamp with the thin filament.

When a wire carries a current, it does not become charged. The movement of electrons in the wire creates the flow of current, but it does not result in a net accumulation of charge on the wire. Therefore, the wire is not charged positively or negatively.

The correct answer is "atoms in the light bulb filament." When an incandescent light bulb is connected to a power source, the electrical current passes through the filament inside the bulb. The filament is usually made of tungsten or another metal that has a high melting point. As the current flows through the filament, it heats up and becomes white-hot, emitting light. The atoms in the filament are responsible for the emission of electrons, which generate the light in the bulb.

The filament of a 100-W light bulb will be thicker compared to the filament thickness of a 60-W light bulb. This is because a higher wattage bulb requires a thicker filament to accommodate the increased electrical current passing through it. The thicker filament helps to prevent overheating and prolong the lifespan of the bulb.

When a light switch is turned on in a DC circuit, the average speed of electrons in the lamp is less than 1 cm/s. This is because in a DC circuit, the flow of electrons is relatively slow compared to other forms of energy transfer, such as the speed of sound waves in metal or the speed of light. The speed of electrons is determined by the voltage and resistance in the circuit, and in most cases, it is much slower than the speed of sound waves or light. Additionally, the speed of electrons is dependent on how quickly each electron bumps into the next electron, which further contributes to the slower average speed.

The power of a light bulb is given by the equation P = V^2/R, where P is the power, V is the voltage, and R is the resistance. Since both light bulbs are rated at the same voltage, the one with a higher power (100-W bulb) must have a lower resistance compared to the 60-W bulb. Therefore, the 60-W bulb has a larger resistance.

The power dissipated in a circuit can be calculated using the formula P = I^2 * R, where P is power, I is current, and R is resistance. In this case, the current is given as 80 A and the resistance is given as 2 ohms. Plugging these values into the formula, we get P = (80 A)^2 * 2 ohms = 12,800 W. Therefore, the correct answer is 12,800 W.

In a series connection, the components are connected in a sequential manner, such that the current flows through one component before reaching the other. Therefore, if one bulb burns out in a series-connected circuit, it breaks the flow of current and causes both headlights to go out. This is different from a parallel connection, where each component has its own separate path for current flow, allowing the other bulb to continue functioning even if one burns out.

When more lamps are added to a series circuit, the overall resistance in the circuit increases. According to Ohm's Law (V = IR), if the resistance increases and the voltage remains constant, the current flowing through the circuit will decrease. Therefore, as more lamps are added in series, the overall current in the power source decreases.

In an AC (alternating current) circuit, the electric field changes magnitude and direction with time. This is because AC circuits have a constantly changing voltage and current, which causes the electric field to vary in strength and direction. As the current alternates between positive and negative values, the electric field also changes accordingly. This is in contrast to a DC (direct current) circuit, where the electric field remains constant in magnitude and direction.

When you turn on the lamp, the filament heats up and becomes incandescent. This causes the electrons in the filament to gain energy and move to higher energy levels. As they return to their original energy levels, they release this excess energy in the form of light. Therefore, the glowing of the lamp comes from the same electrons present in the filament.

The ratio of the potential difference across a metallic conductor to the current in the conductor is known as resistance. Resistance is a measure of how much a material opposes the flow of electric current. It is determined by factors such as the material's resistivity, length, and cross-sectional area. A higher resistance means that a greater potential difference is required to maintain a certain current through the conductor.

The correct answer is "Charge flows in a closed circuit." This statement is correct because in order for electric current to flow, there must be a complete path for the charges to travel, which is provided by a closed circuit. Charge is the fundamental property of matter that carries electric current, and it moves from a higher potential to a lower potential within the circuit. Therefore, charge flowing in a closed circuit is an essential requirement for the flow of electric current.

The correct answer is 110 joules of energy are given up by each coulomb of charge making up the current in the circuit. In a series circuit, the current remains constant throughout, so each coulomb of charge passing through the lamp gives up the same amount of energy. This energy is converted to heat and light in the circuit.

The amount of current in the connecting wire is the same as the amount of current in the filament of a lamp. This is because, in a series circuit, the current remains constant throughout the circuit. Therefore, the current flowing through the filament and the connecting wire is equal.

A capacitor is useful in smoothing pulsed current because it can store electrical energy and release it when needed. When a pulsed current is applied to a circuit, the capacitor charges up during the high points of the pulses and then discharges during the low points, effectively smoothing out the fluctuations in the current. This helps to provide a more stable and consistent flow of current in the circuit.

When lamps are connected in series, the current flowing through each lamp is the same. This is because the current has only one path to follow, and it must pass through each lamp in the series. However, when lamps are connected in parallel, the total current drawn from the battery increases. This is because each lamp in parallel has its own separate path for the current to flow through. Therefore, when the same lamps are connected in parallel, more current is drawn from the battery compared to when they are connected in series.

Touching a faulty 110-volt light fixture is more dangerous than touching a Van de Graaff generator charged to 100,000 volts. This is because the voltage alone does not determine the danger level. The current, which is the flow of electric charge, is what causes harm. A faulty light fixture is connected to a power source and can deliver a high current directly to the body, causing serious injury or even death. On the other hand, the Van de Graaff generator has a high voltage but very low current, making it less dangerous as the current flow is limited.

The primary source of electrons in an ordinary electrical circuit is the electrical circuit itself. When a circuit is closed, electrons flow from the negative terminal of the power source (such as a battery) through the circuit to the positive terminal. The power source provides the initial push to start the flow of electrons, but once the circuit is established, the electrons continue to move within the circuit, driven by the potential difference created by the power source. Therefore, the electrical circuit itself is the source of electrons in a closed circuit.

When two identical light bulbs are connected in series, the total resistance is the sum of the individual resistances. Using Ohm's Law (V = IR), we can rearrange the formula to solve for resistance (R = V/I). In this case, the voltage across both bulbs is 110 V and the current through them is 0.25 A. Plugging in these values, we get R = 110 V / 0.25 A = 440 ohms. However, this is the total resistance of both bulbs. Since they are identical, we divide this value by 2 to find the resistance of a single bulb, which is 440 ohms / 2 = 220 ohms.

When two lamps are connected in parallel to a battery, the electrical resistance that the battery senses is less than the resistance of either lamp. This is because in a parallel circuit, the total resistance is less than the smallest individual resistance. Therefore, the battery senses a lower overall resistance when the lamps are connected in parallel.