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College Physics

1st Edition
Paul Peter Urone + 1 other
ISBN: 9781938168000

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BuyFindarrow_forward

College Physics

1st Edition
Paul Peter Urone + 1 other
ISBN: 9781938168000
Textbook Problem

Consider a 250-W heat lamp fixed to the ceiling in a bathroom. If the filament in one light burns out then the remaining three still work. Construct a problem in which you determine the resistance of each filament in order to obtain a certain intensity projected on the bathroom floor. The ceiling is 3.0 m high. The problem will need to involve concave miners behind the filaments. Your instructor may wish to guide you on the level of complexity to consider in the electrical components.

To determine

The resistance of each filament of a heat lamp in order to obtain certain intensity projected on the bathroom floor.

Explanation

Given info:

The power of the lamp is 250W.

Formula used:

The relation between the current and the power is given as,

I=PV ...... (1)

Here,

  • P is the power of the lamp.
  • V is the voltage applied to the lamp.
  • I is the current.

The expression for the resistance is given as,

R=VI ...... (2)

The magnification is expressed as,

m=dido...... (3)

Here,

  • di is the image distance.
  • do is the object distance.

The expression for the intensity of the radiation is,

I=12PAi ...... (4)

Here,

  • P is the power of the lamp.
  • Ai is the area of the image.

Calculation:

Consider a power of 250W and a voltage of 120V is applied across the parallel combination of four lamps when one lamp gets damage. The distance between the object and the mirror is 30cm and the distance between the mirror and the image is 3.0m . The area of the object is 300cm2.

Substitute 250W for P and 120V for V in equation (1).

I=250W120V=2.1A

Substitute 120V for V and 2.1A for I in equation (2).

R=120V2.1A=57.14Ω

Substitute 30cm for do and 3m for di in equation (3) to calculate the magnification of the object

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