A typical light bulb is 2% efficient. It means that only 2% of electric energy is converted into visible electromagnetic radiation and 98% is converted into ultraviolet radiation known as heat. Suppose a 100W bulb is turned on for 10h.
a. how much energy is used by the lamp? express in kWh.
b. how much energy is wasted due to heat?
c. suppose that the light bulb is turned on for a longer period of time. would you expect its efficiency to increase or decrease?
Please help me...i was absent from class the day we learned this...
I should tell you that the opening statement is wrong. The other 98% percent is infrared (heat) radiation. There is almost no ultraviolet produced. The so called "typical" incandescent light bulbs are no longer in the majority, either.
As far as the questions go, for #1, multiply watts by the number of seconds to get energy produced (in Joules). For #2, (heat only) take 98% of 100 W.
c. Use common sense for #3. Or reread the first sentence of the question.
Sure, I can help you with that. Let's break down each question step by step.
a. To calculate the energy used by the lamp, we need to multiply the power (100W) by the time it is turned on (10h). However, since the power is given in watts and the time in hours, we need to convert the units to kilowatts (kW) and kilowatt-hours (kWh) respectively.
To convert watts to kilowatts, divide by 1000:
100W ÷ 1000 = 0.1kW
Now, we can calculate the energy used in kWh by multiplying the power in kW by the time in hours:
0.1kW × 10h = 1kWh
Therefore, the lamp uses 1 kilowatt-hour (kWh) of energy.
b. Since the light bulb is only 2% efficient, it means that 98% of the electric energy is converted into heat. To calculate the energy wasted due to heat, we need to multiply the energy used by the lamp (1 kWh) by the heat loss percentage (98%):
Heat loss = 98% of 1 kWh = 0.98 × 1 kWh = 0.98 kWh
So, 0.98 kilowatt-hours (kWh) of energy is wasted due to heat.
c. When a light bulb is turned on for a longer period of time, we would not expect its efficiency to increase. Efficiency is a measure of how well a device (in this case, the light bulb) converts energy input into the desired output (visible electromagnetic radiation). The efficiency of a light bulb primarily depends on its design and technological advancements, not the duration it is turned on.
Therefore, the efficiency of a light bulb is generally expected to remain the same regardless of how long it is turned on.
I hope this helps! Let me know if you have any further questions.