NEET Class neet Answered

please answer this

Asked by Prashant DIGHE | 11 Mar, 2020, 10:27: PM

Expert Answer

(1) With S₁ is closed, V₁ = 15 V , V₂ = 20 V

False. When S1 is closed , charge on the plate of 2 pF Capacitor connected to ground is zero, hence voltage across 2 pF capacitor is affected.

Whereas voltage across 3 pF capacitor is unaffected because this capacitor is unaffected.

(2) With S3 is closed V1 =V2 = 25 V . This is false as per explanation given below

Charges on capcitor before and after closing S3 is given below

After closing S3, the net charge in connected plates becomes +30 μC and they are distributed between the two plates

If we consider , voltage across plates equals product of electric field and distance between plates,

Then voltage V₁ across 2 pF capacitor is given by

V₁ = { [ 60 / ( 2 A ε_o ) ] - [ 15 / ( 2 A ε_o ) ] } d = [ (1/2) - (1/8) ] × [ 60 / ( A ε_o ) ] × d = (3/8) 30 V = 11.25 V

Then voltage V₂ across 3 pF capacitor is given by

V₂ = { [ 15 / ( 2 A ε_o ) ] + [ 90 / ( 2 A ε_o ) ] } d = [ (1/12) + (1/2) ] × [ 90 / ( A ε_o ) ] × d = (7/12) 30 V = 17.5 V

(3) with S1 and S2 closed, V1 = V2 = 0 . False

When S1 and S2 is closed, plates connected to earth looses charge , whereas charge on other plates unaffected that gives

some potential difference across plates of capacitors

(4) With S1 and S3 are closed, V1 = 30 V and V2 = 30 V . False statement as explained below

When S1 and S3 are closed, charges on all capacitor plates are getting affected.

Hence original potential differences across capacitors will be affected . Potential differences will not remain same as initial values

Answered by Thiyagarajan K | 13 Mar, 2020, 02:03: PM

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