Number of Resistors needed for a maximum power

[chawki]

Homework Statement

How many resistors, R = 70 ohms can be connected in a series circuit when the maximum power loss of the circuit is 1800W. and the voltages supply is 127V

Homework Equations

Number of resistors!

The Attempt at a Solution

P = V² / x*R
x*7=127²/1800
x=1.28

so only one resistor can be connected.

 

[gneill]

Homework Statement

How many resistors, R = 70 ohms can be connected in a series circuit when the maximum power loss of the circuit is 1800W. and the voltages supply is 127V

Homework Equations

Number of resistors!

The Attempt at a Solution

P = V² / x*R
x*7=127²/1800
x=1.28

so only one resistor can be connected.

Are the resistors 7 Ω or 70 Ω? Your problem statement says 70, but you've used 7 in your calculation.

 

[chawki]

no it's 7 Ohms. sorry for the typing mistake.

 

[SammyS]

Homework Statement

How many resistors, R = 70 ohms can be connected in a series circuit when the maximum power loss of the circuit is 1800W. and the voltages supply is 127V

Homework Equations

Number of resistors!

The Attempt at a Solution

P = V² / x*R
x*7=127²/1800
x=1.28

so only one resistor can be connected.

If R=7Ω , then this is correct !

 

[asteriatic]

I would like to clarify that the equation used in the attempt at a solution is incorrect. The correct equation for power in a circuit is P = V^2/R. Using this equation, we can calculate the maximum power that can be dissipated by a single resistor of 70 ohms in this circuit as P = (127V)^2 / 70 ohms = 231.07W. Since the maximum power allowed in the circuit is 1800W, we can connect a maximum of 1800/231.07 = 7.78 resistors in series. However, since resistors are typically only available in discrete values, we would round down to 7 resistors. Therefore, 7 resistors of 70 ohms can be connected in a series circuit to achieve a maximum power loss of 1800W with a 127V voltage supply.