Current Electricity(12th Grade > Physics ) Questions and Answers
Explanation:-
Answer: Option B. -> 12 cells in series 4 such groups in parallel:
B
Let m cells be connected in series and n such groups are connected in parallel
If the emf of each cell is E and internal resistance r then the total emf of m in series is mE and the total internal resistance is mr. When n such groups are in parallel the effective internal resistance is mr/n. Then the current through an external resistance R is
l=mER+mrn=mnEnR+mr=mnE(√nR−√mr)2+2√mnRr
Now i will be maximum if the denominator is the minimum i.e. if nR=mr
Using R= 3ohm and r=1ohm we have 3n = m
But mn = 48
therefore m×m3=48
which gives m= 12
thus n=4
Explanation:-
Answer: Option B. -> x:
B
The condition for no delflection of the galvanometer is
R1R2=RACRCB
where RAC and RCB are the resistances of the bridge wire of length ACand CBrespectively. If the radius of the wire AB is doubled the ratio
RACRCB will remain unchanged.Hence the balance length will remain the same
Explanation:-
Answer: Option B. -> both the length and the radius of the wire are doubled:
B
Q=V2R
But R=plπr2
Therefore Q=(πV2p)r21
Q is doubled if both l and r are doubled
Explanation:-
Answer: Option B. -> 7 ohm:
B
The circuit can be redrawn as shown in figure. Let a bettery of emf E and of negligible resistance be connected as shown. The current in various branches are shown.Applying Kirchoff's second law to loops ACDA,CBDC and ADBGFA we have
5i2+5i3−10i1=0
10(i2−i3)−5(i1+i3)−i3=0
10i1+5(i1+i3)−E=0
equation (i) and (ii) give i2=3i12 and i3=i12. If R is the effective resistance between A and B
then R=Ei1+i2=2E5i1
from equation (iii) we have
E=15i1+5i3=35i12
R=2E5i1=2∗35i15i1∗2=7 Ohm
Explanation:-
Answer: Option C. -> If a voltmeter is connected across the 6 V battery it will read 7 V:
C
Total resistance = 4 + 1 + 0.5 + 0.5 = 6ohm
Net voltage in the circuit is 6 V
Current l=66=1A in the anticlockwise direction
VPR=1×4=4V
Since R is connected to earth VR=0 hence Vp=4V
VSQ=0.5×1=0.5V
S is at a higher potential than Q
VQ=−0.5V
Current is being forced into the 6 V battery in the opposite direction.Hence V6=E+lr=6+1X
1 = 7 V
Explanation:-
Answer: Option A. -> 44+π ohm:
A
Circumference of the circle = 2πr
Therefore the resistance per unit length of the wire = R2πr
where r= 4 ohm is the resistance of wire
Now the length of the specimen connected along the diameter = 2r
Therefore the resistance of this specimen is
R1=R2πr×2r=Rπ
also the resistance of each semicircle is
R2=R2
equivalent resistance R' across the specimen is given by
1R′=2R+2R+πR=4+πR
R′=R4+π=44+π ohm
Explanation:-
Answer: Option C. -> 48 ohm:
C
If k is the current sensitivity of the galvanometer the current in the galvanometer is
lg=50 K
when a shunt S is connected across it the current through the galavnometer becomes
l′g=lgSG+S=10 K
where G is the resistance of the galvanometer dividing the equations we get
G+SS=5
which gives G=4×S=4×12=48 ohm