Electrical Power and Energy Quiz

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Questions and Answers

What is the formula to calculate current if power and voltage are known?

  • I = E ÷ P
  • I = P ÷ E (correct)
  • I = P x E
  • I = E x P

How many watts does a 1.5 hp motor approximately consume at 28 volts?

  • 746 watts
  • 1,119 watts (correct)
  • 560 watts
  • 1,120 watts

If a resistor dissipates power, what is the direct relationship to current and voltage?

  • Power is proportional to the square of the current and resistance. (correct)
  • Power is constant regardless of current and voltage.
  • Power is independent of resistance.
  • Power is inversely proportional to the voltage and current.

What is the total power consumed by a circuit with a voltage of 12 volts and a current of 20 amps?

<p>240 watts (A)</p> Signup and view all the answers

What describes energy in the context of power calculations?

<p>Stored capacity to perform work (C)</p> Signup and view all the answers

What is the relationship between watts, volts, and amps?

<p>Watts = volts x amps (D)</p> Signup and view all the answers

How many joules of energy does 1 watt provide in 1 second?

<p>1 joule (A)</p> Signup and view all the answers

How long can 1.5 kilojoules of energy provide 25 watts of power?

<p>1 minute (B)</p> Signup and view all the answers

What type of energy is associated with the position or internal state of an object?

<p>Potential energy (A)</p> Signup and view all the answers

What does the principle of conservation of energy state?

<p>Energy is converted from one form to another. (B)</p> Signup and view all the answers

In what form is a battery's energy stored?

<p>Chemical potential energy (C)</p> Signup and view all the answers

When current flows through resistance, what type of energy conversion occurs?

<p>Electrical energy to heat energy (D)</p> Signup and view all the answers

What is the SI unit of energy?

<p>Joule (A)</p> Signup and view all the answers

What is the unit of measurement for power?

<p>Watts (B)</p> Signup and view all the answers

What does the power rating of an electrical component indicate?

<p>The rate at which it converts electrical energy (A)</p> Signup and view all the answers

If a resistor is rated for 3 watts, what is the typical maximum power that should be used?

<p>3 watts (C)</p> Signup and view all the answers

How is power dissipated by a resistor related to its size?

<p>Larger resistors dissipate heat more effectively. (C)</p> Signup and view all the answers

What is the formula for calculating work?

<p>Work (W) = Force (F) x Distance (D) (C)</p> Signup and view all the answers

What is the appropriate power dissipation for a resistor with 6 Volts applied and a current of 100 mA?

<p>0.6 Watts (C)</p> Signup and view all the answers

Which unit is commonly used to measure power in electrical systems?

<p>Watt (W) (B)</p> Signup and view all the answers

Which of the following statements about resistors and their ratings is correct?

<p>Typically, actual power used by a resistor is considerably less than its rating. (D)</p> Signup and view all the answers

What safety factor is typically used when selecting a resistor based on power consumption?

<p>50% (D)</p> Signup and view all the answers

Which of the following correctly describes the relationship between work and power?

<p>Power is the rate at which work is done. (B)</p> Signup and view all the answers

If an engine lifts a weight of 400 lbs over a distance of 10 ft, what is the total work done?

<p>4,000 ft/lbs (A)</p> Signup and view all the answers

Which of the following represents the potential risk for small resistors under high current?

<p>They can overheat quickly. (C)</p> Signup and view all the answers

What happens when voltage is present, but the circuit is open?

<p>No current flows and no work is done. (A)</p> Signup and view all the answers

How does horsepower relate to watts?

<p>1 hp = 746 W (B)</p> Signup and view all the answers

In the SI metric system, what is the unit of work?

<p>Joule (A)</p> Signup and view all the answers

When does work occur in a physical context?

<p>When a force acts on an object and sets it in motion. (A)</p> Signup and view all the answers

What are the three ways to increase the dissipation of heat from a resistor?

<p>Size, airflow, heat sinks (A)</p> Signup and view all the answers

What is the formula for calculating power using current and resistance?

<p>P = I²R (A)</p> Signup and view all the answers

How much power is dissipated when 12 volts are applied to a load drawing 2 amps?

<p>24 watts (C)</p> Signup and view all the answers

If a resistor has a resistance of 20 ohms and carries a current of 4 amps, what is the power dissipated?

<p>320 watts (A)</p> Signup and view all the answers

What is the current draw of two 100-watt driving lights in a car powered by a 12-volt supply?

<p>16.66 amps (D)</p> Signup and view all the answers

What is the maximum power load on a circuit rated for 20 amps at 12 volts?

<p>200 watts (C)</p> Signup and view all the answers

Which of the following correctly states Ohm's Law?

<p>V = IR (B)</p> Signup and view all the answers

What is the relationship between power (P), voltage (E), and current (I)?

<p>P = EI (D)</p> Signup and view all the answers

Flashcards

Power

The amount of energy transferred or converted per unit of time.

Work

The product of force and distance.

Energy

The ability to do work.

Kinetic Energy

Energy associated with motion.

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Potential Energy

Energy stored due to an object's position or state.

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Power Dissipation by a Resistor

The power dissipated by a resistor, calculated as the product of the square of the current and the resistance.

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Watt (W)

A unit of power, equivalent to one joule of energy per second.

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Horsepower (hp)

A unit of power commonly used for engines and motors, equivalent to 746 watts.

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Conservation of Energy

The principle stating that energy cannot be created or destroyed, but only transformed from one form to another.

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Joule

The work done by 1 watt of power in 1 second. Also defined as 1 watt of power radiated or dissipated for 1 second. Measured in Joules.

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Kilowatt

1000 Watts. A unit of power often used for larger energy measurements.

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Power Rating

Indicates the maximum rate at which a device converts electrical energy into another form, like light, heat, or sound.

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Heat Dissipation

The ability of a resistor to lose heat to its surroundings.

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Resistor Power Rating

The maximum power a resistor can handle without overheating or failing.

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Overheating of Small Resistors

A small resistor with limited surface area has trouble dissipating heat, leading to overheating with large currents.

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Efficient Heat Dissipation in Large Resistors

Larger resistors have a greater surface area, allowing for more effective heat dissipation.

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What is power?

The rate at which energy is transferred or converted.

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What is energy?

The ability to do work.

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What is work?

The amount of energy transferred when a force moves an object over a distance.

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What is power dissipation?

The process where a resistor converts electrical energy into heat.

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How do you calculate power?

The formula for power is P = EI, where P is power, E is voltage, and I is current.

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Heat Sinks

A method to increase heat dissipation from a resistor, using specialized components designed to transfer heat away from the resistor.

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Formula wheel

A tool used in electrical calculations, where unknown quantities (represented in the center) are calculated using known values (represented in the surrounding circles) and Ohm's Law and Power Law equations.

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Calculate power dissipation using P=EI

The power dissipated by a load (resistor) is calculated using the equation P = EI, where P is power, E is voltage, and I is current.

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Calculate power dissipation using P=I^2R

The power dissipated by a load (resistor) is calculated using the equation P=I^2R, where P is power, I is current, and R is resistance.

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Calculate current draw

The current draw (amps) of a load can be calculated using the equation I = P/E, where I is current, P is power, and E is voltage.

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Maximum power load

The maximum power load of a circuit is limited by the current rating of the wiring.

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Power (W)

The amount of energy transferred or converted per unit of time is a measure of the rate at which work is done or energy is converted.

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Study Notes

Module 3: Electrical Fundamentals - Topic 3.8: Power

  • Power is defined as the rate at which work is done.
  • The electrical unit of power is the Watt (W).
  • Work is done when a force causes motion. Work is the product of force times distance (W = F x D).
    • Examples include lifting a weight, or moving an object.
    • Units of work are typically foot-pounds (ft/lbs) in the English system and joules (N x m) in the metric system.
    • 1 joule = 1 Newton x 1 metre
  • Energy (kinetic and potential) relates to work.
    • Kinetic energy is associated with motion.
    • Potential energy is associated with position or internal state.
  • A resistor dissipates electrical energy as heat.
  • Power is also the rate of change of electrical energy into another form of energy (such as heat).
  • Power is measured in watts.
  • Power (P) = Voltage (V) x Current (I) or Watts = Volts x Amps.
    • Ohm's law states V=IR (Voltage = Current x Resistance).
    • Combining the 2 equations gives you : P=I^2 * R, or P = V^2 / R
  • The SI unit of energy is the joule. One joule of energy can do one joule of work. One joule of energy could supply one watt of power for one second.
  • Horsepower (hp) is a unit of power. 1 hp equals 746 watts.
  • Components are often rated by maximum power (in watts).
  • A safety factor is typically used in electrical component calculations, and typically is 50%.
  • Heat sinks are used to increase heat dissipation.
  • Size and airflow also contribute to heat dissipation.

Formula Wheel Notes for Power Calculations

  • The formula wheel shows different equations for calculating electrical power, voltage (V), current (I) and resistance (R).
  • These equations are derived from Ohm's Law and Power Law.
    • Note equations for different forms can be used to calculate one unknown if knowns are given
  • Use the wheel to find the appropriate equation.
  • Example calculations are provided in the slides about how to use the formula wheel.

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B - A - 3.8 - Power PDF

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