Electrical Engineering - Ohm's Law - Discussion
Discussion Forum : Ohm's Law - General Questions (Q.No. 23)
23.
A 120 V lamp-dimming circuit is controlled by a rheostat and protected from excessive current by a 3 A fuse. To what minimum resistance value can the rheostat be set without blowing the fuse? Assume a lamp resistance of 20 ohms.
40 
4
2
20
Discussion:
19 comments Page 1 of 2.
Singh said:
3 years ago
Thank you.
Vikas said:
7 years ago
Thanks a lot for explaining the solution.
Suresh said:
8 years ago
Thank you all.
Victor said:
8 years ago
Thank you @Darshan.
(1)
Shivam sahu said:
9 years ago
As resistance is inversely proportional to current. So to calculate minimum resistance we have to consider max. Current through the circuit. So, I=3 A and with the help of this we can find answer as per the mentioned solutions.
Jagadish said:
9 years ago
I got it, Thanks @Raji.
Solayman Hayder said:
9 years ago
We know that, V=IR (ohms law)
Here,
v = 120v.
I = 3A, fuse will work at 3A without burning,
R1= 20ohm, R2=?
R1 + R2 = (120/3) = 40,
R2 = 40 - 20 = 20 ohms (Ans.)
Here,
v = 120v.
I = 3A, fuse will work at 3A without burning,
R1= 20ohm, R2=?
R1 + R2 = (120/3) = 40,
R2 = 40 - 20 = 20 ohms (Ans.)
(6)
Sadbi Ahmad said:
9 years ago
Thank you everybody for solving the solution.
Raji said:
1 decade ago
The fuse rating is 3A. So without blowing the fuse the maximum current can be flown through the circuit is 3A.
When I = 3A, source voltage = 120v.
Resistance = 120/3 = 40 ohms.
So the resistance can be applied from rheostat without damaging fuse = 40-20 = 20 ohms.
When I = 3A, source voltage = 120v.
Resistance = 120/3 = 40 ohms.
So the resistance can be applied from rheostat without damaging fuse = 40-20 = 20 ohms.
(2)
Souvik said:
1 decade ago
We have V=120v and Critical current as 3A.
So the circuit resistance has to be- 120/3 = 40 Ohms.
We have a bulb of 20 Ohms. Hence the rheostat can be set to a minimum of= 40-20 = 20 Ohms.
Answer = 20 Ohms.
So the circuit resistance has to be- 120/3 = 40 Ohms.
We have a bulb of 20 Ohms. Hence the rheostat can be set to a minimum of= 40-20 = 20 Ohms.
Answer = 20 Ohms.
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