What's the Difference Between Potential Difference and EMF in a Solar Cell?

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In summary, the conversation discusses the topic of engineering physics and a specific question about a solar cell's potential difference, internal resistance, EMF, and efficiency. The difference between potential difference and EMF is explained and a suggestion is given to draw a diagram of the system to solve the problem. Efficiency is defined as the ratio of useful energy out to energy in, and a method for calculating it is suggested. The conversation ends with the speaker expressing frustration with their physics class.
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JaeSun
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ok, I am taking engineering physics II ... unfortunately, I am forced to take this as part of my COMPUTER SCIENCE degree ... (why i have no idea..stupid, as i don't really care how many Newtons of force it takes me to push a key on the keyboard, and how much current it takes to go from the keyboard to the computer to put the key on the screen) ... sorry, just I am not the most science-oriented person. which is why I am not a computer engineer.

so i have a question.

the question on my homework is this:

A sloar cell generates a potential difference of 0.10V when a 500-Ohm resistor is connected across it and a potential difference of 0.16V when a 1000-Ohm resistor is substituted. What are (a) the internal resistance and (b) the emf of the sloar cell? (c) The area of the cell is 5.0 (cm^2). What is the efficiency of the cell for converting light energy to internal energy in the 1000-Ohm external resistor?

question. What is the difference between the potential difference, and its emf? i know V=IR . isn't the total V what comes out of the power source? and isn't the emf the power source? I'm lost on what this is.

also, for part c ... how would i approach in solving this? The chapter deals with the circuits, resistors, etc. but effeciency?

any help would be appreciated!
thanks
 
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  • #2
Originally posted by JaeSun


A sloar cell generates a potential difference of 0.10V when a 500-Ohm resistor is connected across it and a potential difference of 0.16V when a 1000-Ohm resistor is substituted. What are (a) the internal resistance and (b) the emf of the sloar cell? (c) The area of the cell is 5.0 (cm^2). What is the efficiency of the cell for converting light energy to internal energy in the 1000-Ohm external resistor?

question. What is the difference between the potential difference, and its emf? i know V=IR . isn't the total V what comes out of the power source? and isn't the emf the power source? I'm lost on what this is.

also, for part c ... how would i approach in solving this? The chapter deals with the circuits, resistors, etc. but effeciency?

thanks

The EMF can be thought of as the Potential Difference at the terminals of the cell WHEN NO CURRENT is flowing. However, the cell has some resistance, so if a current flows through it, then there is a voltage drop inside the cell. The voltage at the terminals will then drop. The emf is the value without this voltage drop, the PD is the Voltage at the terminals when the voltage has dropped (start you car with the lights on and see them dim as the starter turns - that is internal resistance at work). Draw a diagram of the system, including a resistor next to the cell (the internal resistance, r) and then use simple circuit rules to solve it.

Efficiency is the ratio of useful energy out, divided by energy into a system. Work out the solar energy total into the cell and then the energy out.

Hope this helps.
 
  • #3


Originally posted by Adrian Baker


Efficiency is the ratio of useful energy out, divided by energy into a system. Work out the solar energy total into the cell and then the energy out.

Hope this helps.

i am somewhat lost on the last part ... i am going to think that the energy in is 10 mW/(cm^2) ...

but i am lost on how to get the energy going out into the circuit ...

ugh, i hate my physics class...im so lost everyday ...
 

1. What is the difference between qualitative and quantitative data?

Qualitative data is descriptive in nature and is often subjective, while quantitative data is numerical and can be measured. Qualitative data is often used to understand the why and how of a phenomenon, while quantitative data is used to measure and analyze data objectively.

2. How is a hypothesis different from a theory?

A hypothesis is an educated guess or prediction about a phenomenon, while a theory is a well-tested and widely accepted explanation for a phenomenon. A hypothesis can be tested and either proven or disproven, while a theory is supported by a large body of evidence and is considered a reliable explanation.

3. What is the difference between accuracy and precision?

Accuracy refers to how close a measurement is to the true or expected value, while precision refers to how consistent and reproducible a measurement is. In other words, accuracy is about correctness, while precision is about consistency.

4. What is the difference between a control group and an experimental group?

A control group is a group that does not receive any treatment or intervention, while an experimental group is a group that receives the treatment or intervention being tested. The control group is used as a baseline for comparison, and any differences observed in the experimental group can be attributed to the treatment.

5. How does correlation differ from causation?

Correlation refers to a relationship between two variables, where a change in one variable is associated with a change in the other. However, this does not necessarily mean that one variable causes the other. Causation, on the other hand, refers to a direct cause-and-effect relationship between two variables. To establish causation, further research and experimentation are needed to rule out other possible factors.

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