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Ch. 25 - Electric Current and Resistance
Giancoli Douglas - Physics for Scientists and Engineers 5th edition
Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoGiancoli Douglas 5th editionCh. 25 - Electric Current and ResistanceProblema 31
Capitolo 24, Problema 31

An electric car uses a 45-kW (160-hp) motor. If the battery pack is designed for 340 V, what current would the motor need to draw from the battery? Neglect any energy losses in getting energy from the battery to the motor.

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Step 1: Identify the given values in the problem. The power of the motor is given as 45 kW (kilowatts), which can be written as \( P = 45000 \, \text{W} \). The voltage of the battery pack is \( V = 340 \, \text{V} \).
Step 2: Recall the relationship between power, voltage, and current. The formula is \( P = IV \), where \( P \) is power, \( I \) is current, and \( V \) is voltage.
Step 3: Rearrange the formula to solve for current \( I \). This gives \( I = \frac{P}{V} \).
Step 4: Substitute the known values into the formula. Replace \( P \) with \( 45000 \, \text{W} \) and \( V \) with \( 340 \, \text{V} \). The equation becomes \( I = \frac{45000}{340} \).
Step 5: Simplify the expression to find the current \( I \). Perform the division to calculate the current in amperes (A).

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Power in Electrical Circuits

Power in electrical circuits is defined as the rate at which electrical energy is transferred by an electric circuit. It is calculated using the formula P = IV, where P is power in watts, I is current in amperes, and V is voltage in volts. In this context, the motor's power rating of 45 kW indicates how much energy it consumes per unit time.
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Power in Circuits

Ohm's Law

Ohm's Law is a fundamental principle in electronics that relates voltage (V), current (I), and resistance (R) in a circuit. It states that V = IR, meaning the voltage across a conductor is directly proportional to the current flowing through it, provided the temperature remains constant. This law is essential for understanding how current can be calculated when voltage and power are known.
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Resistance and Ohm's Law

Current Calculation

To find the current drawn by an electric motor, we can rearrange the power formula to I = P/V. This means that the current can be determined by dividing the power (in watts) by the voltage (in volts). In this scenario, knowing the motor's power and the battery voltage allows us to calculate the current required for the motor to operate efficiently.
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Intro to Current
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