Uncertain of 2 problems (answers given, but don't know solution-help)

[andreguerra]

Uncertain of 2 problems (answers given, but don't know solution--help!)

1. An electric iron draws 9 amperes from a 120-volt line. The iron's mass is 0.8 kilograms, and it is originally at 20 degrees Celsius. 40% of the heat is lost to the room by radiation. What will the temperature of the iron be 2.0 minutes after it's connected. Assume constant resistance.
Answer is 231 degrees Celsius (note that 60% of power input goes to heating the iron)

2. A drop of water in a fog has a net charge of 200 electrons. What is the radius of the drop if it is suspended motionless on a day when the Earth's electric field is 300 volts/meter?
Answer is radius = 6.16 x 10^-7 meters; hint: electric force must balance weight of drop

Thank you very much!

 

[Doc Al]

Hint for 1: Calculate the electrical energy consumed by the iron in 2 minutes.
Hint for 2: Find the mass of the water drop.

 

[Moetasim]

It appears that you have already been given the answers to these two problems, but are unsure of how to solve them. As a scientist, my advice would be to first understand the concepts involved in these problems. For the first problem, it is important to understand the relationship between power, voltage, current, and resistance, as well as the concept of heat transfer through radiation. Once you have a solid understanding of these concepts, you can use the given information and equations to solve for the temperature of the iron.

Similarly, for the second problem, it is important to understand the concept of electric charge and the relationship between electric force and weight. Once you have a good grasp on these concepts, you can use the given information and equations to solve for the radius of the drop.

If you are still unsure of how to solve these problems, I would recommend seeking help from a teacher or mentor who can guide you through the process and clarify any confusion you may have. Additionally, doing some additional research or practice problems on these topics may also help improve your understanding and ability to solve similar problems in the future. Remember, the key to solving any problem is to have a strong understanding of the underlying concepts and to approach the problem systematically. Best of luck!