Electric Field Strength: 2009 HSC Exam Question Explained | Australia

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Discussion Overview

The discussion revolves around the calculation of electric field strength in the context of a 2009 HSC exam question. Participants explore the implications of different voltage values across charged plates and the correct application of the formula for electric field strength.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant calculates electric field strength as E = 100/0.10 = 1000 and questions the effect of changing the voltage of the positively charged plate to +100V.
  • Another participant corrects the first by stating that electric field strength should be expressed with units, specifically noting it as 1000 V/m.
  • A participant questions the formula E = V/d, proposing that it should be E = 2V/d due to the presence of both positive and negative voltages from a battery.
  • Another participant counters this by stating that the voltage difference across the plates does not equal 20V, clarifying that only the positive terminal is +10V relative to the negative terminal at 0V.

Areas of Agreement / Disagreement

Participants express differing views on the correct application of the electric field strength formula and the interpretation of voltage differences across charged plates. The discussion remains unresolved regarding the proposed formula E = 2V/d.

Contextual Notes

Participants exhibit uncertainty regarding the relationship between voltage and electric field strength, particularly in the context of battery configurations and the reference points for voltage measurements.

123ryoma12
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This is from the 2009 HSC exam. (I'm in Australia)
I checked the answers and found that electric field strength was
E = 100/0.10 = 1000
My question is, what would the electric field strength be if the positively charged plate was +100V instead of 0V
Would it be 200/0.1 = 2000?
Is the formula E = The difference in volts between the two plates / distance.
Please help this has been bugging me.
 
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123ryoma12 said:
E = 100/0.10 = 1000
No it was not. The electric field strength is a dimensionful quantity and you simply cannot quote it as just a number without a unit. The field strength is 1000 V/m = 1 kV/m.

123ryoma12 said:
Would it be 200/0.1 = 2000?
It would be 2000 V/m.
 
I just realized that I shouldn't have posted here. Sorry about that.
But another question
http://www.regentsprep.org/Regents/physics/phys03/aparplate/plate3.gif
In this gif where
E = V/d
Shouldn't it be E = 2V/d
as there is voltage going to the positive and negatively charged plate for example
if the battery has 10V
The negatively charged would be -10V and the positively charge would be 10V
 
123ryoma12 said:
Shouldn't it be E = 2V/d
as there is voltage going to the positive and negatively charged plate for example
if the battery has 10V
The negatively charged would be -10V and the positively charge would be 10V

why would you think that ?
There isn't a 20V difference across the plates
one terminal of the battery, the positive, is +10V relative to the 0V of the negative terminalDave
 
Oh ok thanks. I just thought that for some reason. I didn't really know how the battery worked.
 
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