Page 20 - Physics - XII

Principle/Theory K

If two or more resistances + –
say R , R , ....... are connected X E X R Rheostat
1
2
in series as shown Fig. 3(a).2, 1 2
then their combined resistance B RB
R of the series combination is E F
S
given as G
R = R + R + _____
1
S
2
The value of an unknown 0 10 20 30 40 50 60 70 80 90 100
resistance X can be determined Q D P
by using metre bridge as Jockey (J)
A C
l l cm (100–l) cm
X = R
100 l Fig. 3 (a). 1: Circuit diagram for series combination of resistors

R R
where l is the length of metre bridge wire from zero end to 1 2
balance point and R is the resistance from resistance box.
Fig. 3 (a). 2: Series combination
Procedure
1. Take two resistances.
2. Adopt the same steps as in experiment 2 to determine the values of X and X one by one.
1
2
3. Now, connect the resistances X and X in series as shown in Fig. 3(a).1 in the left gap of the metre
2
1
bridge and fi nd the resistance of the combination X . Take at least three sets of observation and record
S
them in the observation table.
Observations and Calculations

Table for calculation of resistances X , X , and X
1 2 S
Resistance Length Length DC Resistance Mean
Resistance used S. from resistance AD = l = (100 – l) X l R resistance
100
in the left gap No. box, R (cm) (cm) l X
(Ω) (Ω) (Ω)

1.
X 2. X =
1 1
3.
1.
X 2. X =
2 2
3.
1.
X and X in
1 2 2. X =
series S
3.

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