# Electric field strength from a light bulb

• A90
In summary, to find the electric field strength of the electromagnetic waves radiated by a 100-W light bulb at a distance of 3.0m, we need to consider the flux of electromagnetic energy through a sphere of radius 3.0 m and relate that to the amplitude of the electric field in the electromagnetic plane wave. The equation used is $$\vec{E}=\frac{kq}{d^{2}}$$ and to solve for q, we can use the equation $$q=\sqrt{\frac{3Pc^{3}}{2ka^{2}}}$$, but we still need to find the acceleration, which can be obtained by considering the flux of electromagnetic energy.
A90

## Homework Statement

What is the approximate electric field strength of the electromagnetic waves radiated by a 100-W light bulb, measured 3.0m from the bulb?

## Homework Equations

$$\vec{E}=\frac{kq}{d^{2}}$$

$$P=\frac{2kq^{2}a^{2}}{3c^{3}}$$

## The Attempt at a Solution

I solved for ##q=\sqrt{\frac{3Pc^{3}}{2ka^{2}}}##, and then plugged that into the equation for electric field, and I have all the values I need to solve except for the acceleration, which I'm not sure how to find. I thought about using the second derivative of ##x(t)= x~sin(\omega~t)##, but I don't know what to use for ##x##, ##\omega## or ##t##.

Last edited by a moderator:
Your model assumes that lightbulb filaments produce light by having a monopole charge ##q## that radiates energy. That's not how light bulbs work. For this calculation, you need to consider the flux of electromagnetic energy through a sphere of radius 3.0 m and relate that flux to the amplitude of the electric field in the electromagnetic plane wave that crosses the sphere.

Edited to correct typo.

Last edited:
tech99

## What is electric field strength?

Electric field strength is a measure of the force exerted by an electric field on a unit charge at a particular point in space. It is represented by the symbol E and is measured in volts per meter (V/m).

## How is electric field strength related to a light bulb?

Electric field strength can be generated by a light bulb when it is turned on. The electric field is created by the movement of charged particles, such as electrons, through the wires and filament of the light bulb.

## Does the electric field strength vary with distance from the light bulb?

Yes, the electric field strength decreases as you move further away from the light bulb. This is because the electric field follows an inverse-square law, meaning the strength decreases as the distance squared.

## Can the electric field strength from a light bulb be measured?

Yes, the electric field strength from a light bulb can be measured using a device called an electric field meter. This device detects the electric field and gives a numerical reading in volts per meter.

## Are there safety concerns related to the electric field strength from a light bulb?

Generally, the electric field strength from a light bulb is not strong enough to pose a safety risk. However, it is important to follow proper handling and usage guidelines for light bulbs to avoid any potential hazards.

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