# Need help on Electric Field Questions

• tachu101
In summary, the conversation involves a student seeking help with difficult questions for their homework due tomorrow. The questions involve calculating wasted energy and power in a toaster, kinetic energy and velocity of electrons fired from an electron gun, and electric field and potential difference between two students in a spark experiment. The student is struggling with understanding the concepts and equations involved in solving these problems.
tachu101
These are a few of the harder questions from my homework that is due tomorrow. Please Help.

## Homework Statement

A) How much energy is wasted when 35C of charge flows through a 120V toaster in 5 sec? How much power?

B) An electron gun fires electrons from rest and smashes them into a screen that is .33m away. The accelerating voltage that causes this is 2850V.
1. What is the kinetic energy?
2. What is the velocity right before impact
3. What is the magnitude and direction of the electric field accelerating the electron?
4. What is the force experienced by the accelerating electron?
5. how much time does in take for the electron to make this trip?

C) Two opposite charged students bring their fingers towards each other and a spark jumps between their fingers at 7 cm apart. What is the electric field in the region between their fingers when the spark occurs. What is the potential difference between the two students (in voltage)?

V=ed
W=qed
P=IV
KE=1/2mv^2

## The Attempt at a Solution

I am really confused with these questions.

For the first one I have 840Watts and 4200J for the toaster

I don't get the electron gun one.

The spark one is equally confusing, we were given that the Emax in air is 3*10^6J, but I do not know if this is needed for this question.

You got the first one right. Though I wouldn't describe the energy as 'wasted'. Toasters are supposed to heat up. For the second one you have to try harder. Volts are joules/coulomb. How much energy does one coulomb gain passing through the potential difference? How many electrons in a coulomb? What's the energy in a single electron? Etc. For the last one I don't understand your given. What is Emax supposed to mean if it's an energy? If it's an electric field then the units are wrong.

Dear student,

Thank you for reaching out for help with your electric field questions. I understand that these concepts can be challenging, but with some guidance and practice, you can master them.

For the first question, you are correct in your calculations for the energy and power of the toaster. To calculate the wasted energy, you can use the equation W=QV, where Q is the charge (35C) and V is the voltage (120V). This will give you the same answer of 4200J. For the power, you can use the equation P=IV, where I is the current (Q/t) and V is the voltage. This will give you 840W, as you already calculated.

Moving on to the electron gun question, let's break it down into smaller parts. First, we need to calculate the acceleration of the electron. This can be done using the equation a=V/d, where V is the voltage (2850V) and d is the distance (0.33m). This will give you an acceleration of 8636.36 m/s^2. Next, we can use the equation v^2=u^2+2as, where u is the initial velocity (0 m/s), a is the acceleration we just calculated, and s is the distance between the gun and the screen (0.33m). This will give you a velocity of 1631.92 m/s right before impact.

Now, to find the kinetic energy, we can use the equation KE=1/2mv^2, where m is the mass of the electron (9.11*10^-31 kg) and v is the velocity we just calculated. This will give you a kinetic energy of 1.38*10^-17 J.

To find the magnitude and direction of the electric field accelerating the electron, we can use the equation F=ma, where m is the mass of the electron and a is the acceleration we calculated earlier. This will give you a force of 8.83*10^-28 N. The direction of the electric field will be in the direction of the acceleration, which will be towards the screen.

To calculate the time it takes for the electron to make this trip, we can use the equation t=d/v, where d is the distance (0.33m) and v is the velocity we calculated earlier. This will give you a time of 2.02

## 1. What is an electric field?

An electric field is a region in which an electrically charged particle experiences a force. It is created by electric charges and is measured in units of volts per meter (V/m).

## 2. How do you calculate the electric field?

The electric field at a point is calculated by dividing the force experienced by a test charge at that point by the magnitude of the test charge. Mathematically, it is represented as E = F/q, where E is the electric field, F is the force, and q is the test charge.

## 3. What is the difference between electric potential and electric field?

Electric potential is the amount of work needed to move a unit of positive charge from one point to another in an electric field, while electric field is the force experienced by a charged particle at a given point. In simpler terms, electric potential is the potential energy per unit charge, and electric field is the force per unit charge.

## 4. Can an electric field exist without charges?

No, an electric field cannot exist without charges. Charges are the source of electric fields and without them, there would be no force or field present.

## 5. How does distance affect the strength of an electric field?

The strength of an electric field decreases as the distance from the source charge increases. This is due to the inverse-square law, which states that the strength of the electric field is inversely proportional to the square of the distance from the source charge.

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