Electrical Instruments

The deflection in galvanometer falls to ${\left(\frac{1}{4}\right)}^{th}$, when it is shunted by $3 \Omega$ . If additional shunt of $\mathrm{2 \Omega }$ is connected in parallel to earlier shunt, the deflection in galvanometer falls to ${\left(\frac{1}{\alpha }\right)}^{th}$ value. Write the value of $2\alpha$.

A moving coil galvanometer has the following characteristics- Number of turns of coil$=50$, Area of coil$=70{\mathrm{mm}}^2$, Resistance of coil$=30 \Omega$, the flux density of radial field$=0.1\mathrm{T}$, Torsional constant of suspension wire$=7\times {10}^{-8}\mathrm{Nm}/\mathrm{rad}$. Calculate the voltage sensitivity. 

The voltage sensitivity is defined as the deflection per unit current.

What is the SI unit of the voltage sensitivity?

Write the expression of the voltage sensitivity.

A moving coil galvanometer produces deflection $20.5\mathrm{rad}$ for current $10\mathrm{\mu A}$. Calculate current sensitivity?

The SI unit of current sensitivity in galvanometer is

A convenient way for the manufacturer to increase the current sensitivity is to increase the number of turns in the galvanometer.

Write the expression for the sensitivity of the ammeter.

If an ammeter is to be used in place of a voltmeter, then with the ammeter we must connect a,

What resistance should be connected in series of a galvanometer of resistance $R_g$ in order to change its range from $V$ volts to $N\mathrm{V}$ volts (in $\mathrm{ohm}$)

A voltmeter has a $25 \mathrm{\Omega }$ coil and $575 \mathrm{\Omega }$ in series. The coil takes $10\mathrm{ }\mathrm{m}\mathrm{A}$ for full-scale deflection. The maximum potential difference which can be measured is 

The combined resistance of galvanometer of resistance $1000 \mathrm{\Omega }$ and its shunt is $25 \mathrm{\Omega }$. Calculate the value of shunt.

A resistance of $3 \mathrm{\Omega }$ is connected in parallel to a galvanometer of resistance $297 \mathrm{\Omega }$. Find the fraction of current passing through galvanometer.

A galvanometer has a resistance of $16 \mathrm{\Omega }$ and gives a full scale deflection when a current of $20 \mathrm{mA}$ is passed through it. The only shunt resistance available is $0.04 \mathrm{\Omega }$ which is not appropriate to convert galvanometer into an ammeter. How much resistance should be connected in series with coil of galvanometer so that the range of ammeter is $10 \mathrm{A}$?

Calculate the value of resistance needed to convert a moving coil galvanometer of $60 \mathrm{\Omega }$ into an ammeter of range $5 \mathrm{A}$ which gives full scale deflection for a current of $50 \mathrm{mA}$ and into voltmeter of range $0-50 \mathrm{V}$.

A galvanometer with a coil of resistance $40 \mathrm{\Omega }$ gives a full scale deflection for a current of  $5 \mathrm{mA}$. How will you convert it into an ammeter of range $0-5\mathrm{A}$?

Explain how a moving coil galvanometer is converted into voltmeter. Derive the necessary formula.

Explain how a moving coil galvanometer is converted into an ammeter. Derive the necessary formula.