Calculating Full-Scale Deflection for Weakened Magnetic Field?

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In summary, the needle of a moving coil meter gives a full-scale deflection for a current of 50uA. If the magnetic field weakened to 80% of its original value, a full-scale deflection would result in 20% more current than before, resulting in 60uA. However, due to the non-linear relationship between magnetic field and current, the actual answer is 63uA. This highlights the importance of understanding the underlying principles and not relying solely on intuition in problem-solving.
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pivoxa15
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Homework Statement


The needle of a moving coil meter gives a full-scale deflection for a current of 50uA. What current would give a full-scale deflection if the magnetic field weakened to 80% of its original value?


Homework Equations





The Attempt at a Solution


Decrease magnetic field => needle not deflected as much for a given current such as 50uA. A full-scale deflection now would result in 20% more current than before because of the 20% decrease in magnetic field. I assume the powers of magnetic strength and current are equal and unity. So now 50uA*1.2=60uA would result. However the answers suggested 63uA. Why?
 
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  • #2
Because "a 20% decrease" and a "20% increase" are not the inverse of each other.

0.8 times 1.2 = 0.96, not 1.0

Your basic idea about how to solve the problem is OK.
 
  • #3
That is good. It's liitle things like this that tests your mathematical intuition. For me, it's obviously not very good but I'm working on it.
 

FAQ: Calculating Full-Scale Deflection for Weakened Magnetic Field?

What is full-scale deflection?

Full-scale deflection is a term used in engineering and physics to describe the maximum displacement or deformation of a structure or object under a given load or stress.

How is full-scale deflection measured?

Full-scale deflection is typically measured using a variety of techniques, such as strain gauges, displacement sensors, and laser interferometry, depending on the specific application and type of structure being tested.

What causes full-scale deflection?

Full-scale deflection can be caused by a number of factors, including external loads, internal stresses, and material properties. It can also be influenced by environmental factors, such as temperature and humidity.

Is full-scale deflection the same as failure?

No, full-scale deflection is not necessarily the same as failure. While a structure or object may reach its maximum deflection without experiencing any permanent damage, failure occurs when it is unable to support the applied load or stress and becomes permanently deformed or breaks.

How can full-scale deflection be minimized?

Full-scale deflection can be minimized by designing structures and objects with appropriate materials, dimensions, and reinforcement to withstand the expected loads and stresses. Regular maintenance and monitoring can also help prevent excessive deflection.

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