Electromagnetism homework question

We get:I = Emf/R = -0.0245V/(2.8x10^-3Ω) = -8.75ASince current cannot be negative, we take the absolute value and get a final answer of 8.75A for the current in the loop. In summary, to determine the current in the loop, we used Faraday's Law and the formula for magnetic flux to calculate the induced emf, which we then used to find the current in the loop using Ohm's Law.
  • #1
gillgill
128
0
1. A simple generator has a 200-loop square coil 25.0cm on a side. How fast must it turn in a 0.550T field to produce a 120V peak output?

area=(0.25)^2
=6.25x10^-2

E=-N(BA)/t
t=-(300)(6.25x10^-2)(0-0.550T)/120V
t=8.6x10^-2 s
do you need to times it by 4 to get the time for one rotation??

2. A motor has an armature resistance of 3.40ohms. If it draws 8.70A when running at full speed and connected to a 120V line, how large is the counter emf?
V-Ir-Emf=0
Emf=V-Ir
=120-(8.7)(3.4)
=90.4V
Is this right?

3. A 30cm diameter coil consists of 30 turns of circular copper wire 2.8mm in diameter. A uniform magnetic field, perpendicular to the plane of the coil, changes at a rate of 8.65x10^-3T/s. Determine the current in the loop.

I have no idea how to start this question.
Plz help...thx...
 
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  • #2


Hi there! I can help you with these questions. Let's take a look at them one by one.

1. To calculate the speed of the generator in a magnetic field, we need to use the formula E = NABω, where E is the voltage output, N is the number of loops in the coil, A is the area of the coil, B is the magnetic field strength, and ω is the angular velocity (or speed) of the generator. We also know that E = 120V and A = (0.25)^2 = 0.0625 m^2. Plugging these values into the formula, we get:

120V = (200)(0.0625 m^2)(0.550T)ω

Solving for ω, we get ω = 174.545 radians/s. To get the speed in rotations per second, we need to divide by 2π, so the generator needs to turn at a speed of 27.75 rotations per second.

2. Your calculation for the counter emf is correct. To check, we can also use the formula Emf = V - I(R), where V is the voltage, I is the current, and R is the resistance. Plugging in the values given, we get:

Emf = 120V - (8.7A)(3.4Ω) = 90.4V

So your answer is correct!

3. To solve this question, we can use Faraday's Law, which states that the induced emf in a loop is equal to the rate of change of magnetic flux through the loop. In other words, we can use the formula Emf = -N(dΦ/dt), where N is the number of turns in the coil and dΦ/dt is the rate of change of magnetic flux. We also know that the magnetic flux through a circular coil is given by Φ = BA, where B is the magnetic field strength and A is the area of the coil. Plugging these values into the formula, we get:

Emf = -(30)(8.65x10^-3T/s)(π(0.15m)^2)

Solving for Emf, we get Emf = -0.0245V. We know that Emf = IR, so we can rearrange this equation to solve for I, the current in the loop
 
  • #3


1. Yes, you are correct. To find the time for one rotation, you would need to multiply by 4. This is because the coil has 4 sides, so it will go through 4 rotations for each full rotation of the generator.

2. Your calculation for the counter emf is correct. Keep in mind that the units for resistance are ohms, not volts, so your final answer should be 90.4V.

3. To find the current in the loop, you can use Faraday's Law of Electromagnetic Induction: E=-N(dB/dt), where E is the induced emf, N is the number of turns in the coil, and (dB/dt) is the rate of change of the magnetic field. In this case, E=0 since the loop is open, so we can rearrange the equation to solve for the current: I=-E/R. The resistance of the loop can be calculated using the formula R=ρL/A, where ρ is the resistivity of copper, L is the length of the wire, and A is the cross-sectional area. Once you have the resistance, you can plug it into the equation for current to find the answer.
 

What is electromagnetism?

Electromagnetism is the branch of physics that deals with the study of electromagnetic forces and their interactions with matter.

What is the difference between electric and magnetic fields?

Electric fields are created by stationary electric charges, while magnetic fields are created by moving electric charges or changing electric fields.

How do I calculate the strength of an electromagnetic field?

The strength of an electromagnetic field is determined by the magnitude of the electric and magnetic fields at a given point. This can be calculated using the equations for electric and magnetic fields, as well as the properties of the source of the fields.

What is the relationship between electricity and magnetism?

Electricity and magnetism are closely related phenomena. Moving electric charges generate magnetic fields, and changing magnetic fields can induce electric currents. This relationship is described by Maxwell's equations.

How is electromagnetism used in everyday life?

Electromagnetism has countless practical applications in everyday life, including electric motors, generators, televisions, radios, and many other electronic devices. It is also used in medical imaging, communication technologies, and transportation systems.

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