Electrical Engineering: Basic Laws (5 of 31) Finding R=? (Resistance) in an Element

Michel van Biezen
31 Oct 201505:31

Summary

TLDRThis video tutorial explains how to calculate the resistance of electrical components like resistors or lightbulbs. It outlines two methods: one using Ohm's law with given voltage and current, and another using the power equation when power and voltage are known. The video demonstrates calculations for both a 100-watt and a 60-watt lightbulb connected to a 120-volt source, revealing that resistance increases with lower power consumption.

Takeaways

  • ๐Ÿ’ก Ohm's Law states that resistance (R) is equal to voltage (V) divided by current (I), represented as R = V/I.
  • ๐Ÿ”Œ Example: If a voltage of 120 volts and a current of 5 amps are given, the resistance is 24 ohms.
  • ๐Ÿ”‹ In a circuit where both voltage and power are known, resistance can also be calculated using the power equation.
  • โšก The power equation states that power (P) is equal to the current squared (I^2) multiplied by the resistance (R).
  • ๐Ÿ” The current can be found using the equation I = P/V when both power and voltage are known.
  • ๐Ÿ’ก Example: For a 100-watt light bulb connected to a 120-volt source, the current is 0.833 amps.
  • ๐Ÿ“ Resistance for the 100-watt light bulb is calculated as 144 ohms using the equation R = P/Iยฒ.
  • ๐Ÿ’ก A 60-watt light bulb connected to the same voltage source (120 volts) draws 0.5 amps of current.
  • ๐Ÿ“ The resistance for a 60-watt light bulb is higher at 240 ohms, showing that lower wattage light bulbs have higher resistance.
  • ๐Ÿ”„ Lower resistance results in higher current, which leads to more power consumption, explaining why higher-wattage bulbs use more power.

Q & A

  • What is the formula used to find resistance when both current and voltage are given?

    -The formula used is Ohm's law, which is R = V / I, where R is resistance, V is voltage, and I is current.

  • How do you calculate the resistance when the current is 5 amps and the voltage is 120 volts?

    -Using the formula R = V / I, you would calculate the resistance as R = 120V / 5A, which equals 24 ohms.

  • What is the approach when you are given power and voltage instead of current?

    -You use the power equation P = I * V, and Ohm's law (I = V / R) to find the current and then use the formula R = P / Iยฒ to calculate resistance.

  • How do you calculate the current if the power is 100 watts and the voltage is 120 volts?

    -The current I is calculated using the formula I = P / V, so I = 100W / 120V = 0.833 amps.

  • Once you know the current, how do you calculate the resistance for a 100-watt light bulb?

    -Using the formula R = P / Iยฒ, with P = 100 watts and I = 0.833 amps, the resistance is calculated as R = 100 / (0.833ยฒ), which equals 144 ohms.

  • Why does a 60-watt light bulb have a higher resistance than a 100-watt light bulb?

    -A 60-watt bulb has a higher resistance because it draws less current for the same voltage. Higher resistance leads to lower current, resulting in lower power consumption.

  • How do you calculate the resistance for a 60-watt light bulb?

    -First, calculate the current using I = P / V, so I = 60W / 120V = 0.5 amps. Then, using R = P / Iยฒ, the resistance is R = 60 / (0.5ยฒ) = 240 ohms.

  • What is the relationship between power, current, and resistance in a circuit?

    -The power consumed in a circuit is related to the current and resistance by the equation P = Iยฒ * R. Higher resistance results in lower current and lower power consumption for a given voltage.

  • How does the resistance of a device affect the current it draws?

    -A higher resistance results in a lower current, while a lower resistance allows more current to flow through the device for the same voltage.

  • What is the general method to calculate the resistance of an electrical device using power and voltage?

    -First, calculate the current using I = P / V. Then, use the formula R = P / Iยฒ to find the resistance.

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Related Tags
Ohm's lawresistance calculationelectric circuitscurrent voltagepower consumptionlight bulb resistanceelectronics tutorialcircuit analysisphysics learningengineering basics