Physics current electricity

Please Wait... While Loading Full Video

current electricity

Galvanometer

It is an instrument used to detect small current passing through it by showing deflection. Galvanometers
are of different types e.g. moving coil galvanometer, moving magnet galvanometer, hot wire galvanometer.
In DC circuit usually moving coiI galvanometer are used.
(i) Full scale deflection current: The current required for full scale deflection in a galvanometer is called
full scale deflection current and is represented by `i_g`,
(ii) Shunt : The small resistance connected in parallel to galvanometer coil, in order to control current
flowing through the galvanometer is known as shunt.

It is an instrument used to detect small current passing through it by showing deflection. Galvanometers
are of different types e.g. moving coil galvanometer, moving magnet galvanometer, hot wire galvanometer.
In DC circuit usually moving coiI galvanometer are used.
(i) Full scale deflection current: The current required for full scale deflection in a galvanometer is called
full scale deflection current and is represented by `i_g`,
(ii) Shunt : The small resistance connected in parallel to galvanometer coil, in order to control current
flowing through the galvanometer is known as shunt.

Ammeter:

(i) The reading of an ammeter is always lesser than actual current in the circuit.
(ii) Smaller the resistance of an ammeter more accurate wi ll be its reading. An ammeter is said to be ideal
if its resistance r is zero.

`text(Conversion of galvanometer into ammeter: )`
A galvanometer may be converted into an ammeter
by connecting a low resistance (called shuntS) in parallel to the galvanometer Gas shown in figure.

(a) Equivalent resistance of the combination =`(GS)/(G + S)`
(b) G and S are parallel to each other hence both will have equal potential difference i.e.` i_g G = (i - i_g)S;`
which gives Required shunt` S =i_g G/ (i-i_g)`
(c) To pass nth part of main current `(i.e. i_g = i/n)` through the galvanometer, required shunt `S =G/ (n - 1)`
(d) As we increase the range of ammeter using the same galvanometer shunt resistance should be decrease ie resistance of ammeter will decrease hence accuracy will increase.

(i) The reading of an ammeter is always lesser than actual current in the circuit.
(ii) Smaller the resistance of an ammeter more accurate wi ll be its reading. An ammeter is said to be ideal
if its resistance r is zero.

`text(Conversion of galvanometer into ammeter: )`
A galvanometer may be converted into an ammeter
by connecting a low resistance (called shuntS) in parallel to the galvanometer Gas shown in figure.

(a) Equivalent resistance of the combination =`(GS)/(G + S)`
(b) G and S are parallel to each other hence both will have equal potential difference i.e.` i_g G = (i - i_g)S;`
which gives Required shunt` S =i_g G/ (i-i_g)`
(c) To pass nth part of main current `(i.e. i_g = i/n)` through the galvanometer, required shunt `S =G/ (n - 1)`
(d) As we increase the range of ammeter using the same galvanometer shunt resistance should be decrease ie resistance of ammeter will decrease hence accuracy will increase.

Voltmeter:

It is a device used to measure potential difference and is always put in parallel with the
'circuit element' across which potential difference is to be measured.

(i) The reading of a voltmeter is always lesser than true value.
(ii) Greater the resistance of voltmeter, more accurate will be its reading. A voltmeter is said to be ideal
if its resistance is infinite, i.e., it draws no current from the circuit element for its operation.

`text(Conversion of galvanometer into voltmeter:)`
A galvanometer may be converted into a voltmeter
by connecting a large resistance R in series with the galvanometer as shown in the figure.
(a) Equivalent rcsistanceofthecombination = G + R
(b)Aecording to ohm's law` = i_g (G+ R) ;` which givesrequired series resistance `R = v/i_g - G = (v/v_g - 1)G`
(c) If `n^(th)` part of applied voltage appeared across galvanometer `(i.e. v_g = v/n)` then required series resistance
`R = (n-1)G.`
(d) As we increase the range of voltmeter using the same galvanometer series resistance should be increased ie resistance of voltmeter will increase hence accuracy will increase.

It is a device used to measure potential difference and is always put in parallel with the
'circuit element' across which potential difference is to be measured.

(i) The reading of a voltmeter is always lesser than true value.
(ii) Greater the resistance of voltmeter, more accurate will be its reading. A voltmeter is said to be ideal
if its resistance is infinite, i.e., it draws no current from the circuit element for its operation.

`text(Conversion of galvanometer into voltmeter:)`
A galvanometer may be converted into a voltmeter
by connecting a large resistance R in series with the galvanometer as shown in the figure.
(a) Equivalent rcsistanceofthecombination = G + R
(b)Aecording to ohm's law` = i_g (G+ R) ;` which givesrequired series resistance `R = v/i_g - G = (v/v_g - 1)G`
(c) If `n^(th)` part of applied voltage appeared across galvanometer `(i.e. v_g = v/n)` then required series resistance
`R = (n-1)G.`
(d) As we increase the range of voltmeter using the same galvanometer series resistance should be increased ie resistance of voltmeter will increase hence accuracy will increase.

SiteLock