Physics · Practical apparatus

Galvanometer half deflection

Adjust a shunt until deflection is half the unshunted reading. Then use the finite series-resistance correction to infer coil resistance and use original current per division for figure of merit.

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Galvanometer half deflection

இணை மின்தடையை மாற்றி திருப்பம் பாதியாக்கவும். G=SR/(R−S) மூலம் கம்பிச்சுருள் மின்தடை பெறலாம்.

Key notes, relationships and model limits

Key relationship

At exact half deflection G=SR/(R−S); k=ε/[(R+G)θ].

Practical tip

Adjust a shunt until deflection is half the unshunted reading. Then use the finite series-resistance correction to infer coil resistance and use original current per division for figure of merit.

Common trap

The exact half-deflection expression includes the finite series resistance; G ≈ S is a limiting approximation.

Model limits

linear galvanometer, ideal cell and resistors; inferred G applies only at half deflection. If R≤S, readout explicitly marks inference invalid.

What you will learn

Adjust galvanometer half deflection apparatus, observe its reading and derive the indicated physical quantity.

Try the experiment

Try both scenarios, change one control, and predict the result before checking the graph and readouts.

Think of it this way

Change one input while keeping the others fixed, as you would in a controlled experiment.

Worked example

For G=100 Ω and R=2000 Ω, exact half-deflection S=GR/(G+R)≈95.238 Ω.

Why this matters

The model connects galvanometer half deflection with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

Half-deflection inference G=SR/(R−S) requires?

R smaller than S.
R greater than S and an actual half reading.
Any shunt value, even without a half reading.

Read the explanation

R greater than S and an actual half reading.

Course connection: Virtual apparatus preparation. Check exact board/exam membership in the syllabus sources. Physical practical work remains necessary.