Question

Conduct this experiment to determine the combined heat transfer coefficient between an incandescent lightbulb and the surrounding air and surfaces using a 60 -W lightbulb. You will need a thermometer, which can be purchased in a hardware store, and metal glue. You will also need a piece of string and a ruler to calculate the surface area of the lightbulb. First, measure the air temperature in the room, and then glue the tip of the thermocouple wire of the thermometer to the glass of the lightbulb. Turn the light on and wait until the temperature reading stabilizes. The temperature reading will give the surface temperature of the lightbulb. Assuming 10 percent of the rated power of the bulb is converted to light and is transmitted by the glass, calculate the heat transfer coefficient from Newton's law of cooling.

Short answer

Short Answer: To find the combined heat transfer coefficient between an incandescent lightbulb and the surrounding air and surfaces, you need to follow these steps: 1. Measure the air temperature (T_air) and the lightbulb's surface temperature (T_surface) with a thermometer. 2. Determine the power output in the form of heat (P_heat) by calculating 90 percent of the bulb's rated power (e.g., for a 60W bulb, P_heat = 54 watts). 3. Calculate the surface area (A) of the lightbulb, approximating it as a sphere. 4. Use Newton's law of cooling formula, Q = h * A * (T_surface - T_air), and the power output in the form of heat (P_heat) to calculate the heat transfer coefficient (h). Once you've calculated the value of h, you've found the combined heat transfer coefficient between the incandescent lightbulb and the surrounding air and surfaces.

Step-by-step solution

Measure the air temperature

Using a thermometer, measure the temperature of the surrounding air in the room. Record this value as T_air.

Attach the thermocouple to the lightbulb

Apply metal glue to the tip of the thermocouple wire of the thermometer and attach it to the glass surface of the lightbulb. Wait for the glue to cure according to the manufacturer's instructions.

Turn on the light and measure the surface temperature

After the glue is cured, turn on the light and wait until the temperature reading on the thermometer stabilizes. This value represents the surface temperature of the lightbulb. Record this value as T_surface.

Determine the power output in the form of heat

Since only 10 percent of the bulb's rated power (60 watts) is converted to light and is transmitted by the glass, we can determine the power output in the form of heat by calculating 90 percent of 60 watts. P_heat = (90/100) * 60 = 54 watts

Calculate the surface area of the lightbulb

Using the piece of string and ruler, measure the circumference and diameter of the lightbulb. The lightbulb can be approximated as a sphere. Calculate the surface area (A) of the lightbulb using the formula for the surface area of a sphere: A = 4 * pi * (radius^2)

Calculate the heat transfer coefficient using Newton's law of cooling

Newton's law of cooling states that the heat transfer rate (Q) is proportional to the temperature difference between the surface (T_surface) and the surrounding air (T_air), with the proportionality constant being the heat transfer coefficient (h) and the surface area (A): Q = h * A * (T_surface - T_air) We have calculated the power output in the form of heat (P_heat) and the surface area (A), so we can solve for the heat transfer coefficient (h): h = Q / (A * (T_surface - T_air)) Since Q = P_heat = 54 watts, and we already determined A and measured T_air and T_surface: h = 54 / (A * (T_surface - T_air)) Once you've calculated h, you've found the combined heat transfer coefficient between the incandescent lightbulb and the surrounding air and surfaces.