Electrical Engineering - Ohm's Law - Discussion
Discussion Forum : Ohm's Law - General Questions (Q.No. 12)
12.
You are measuring the current in a circuit that is operated on an 18 V battery. The ammeter reads 40 mA. Later you notice the current has dropped to 20 mA. How much has the voltage changed?
Discussion:
29 comments Page 2 of 3.
Estrellanes said:
9 years ago
The half of 40 is 20, and the half of 18 is 9. So the answer is A) 9v.
S k s said:
9 years ago
Voltage change 18 - 9 = 9 volt.
Roderick acuesta said:
9 years ago
The problem is not clear because not tell if the load is variable.
Vinodroyal said:
9 years ago
If current increase voltage decreases.
Krishna said:
9 years ago
Or you can say V is directly proportional to I. So when the current drops so as the voltage.
HARDIK said:
10 years ago
V = 18 v, I = 40 mA, R = ?
V = IR.
R = V/I.
= 18/40*10^-3.
= (18/40)*10^3.
= 18000/40.
= 450 ohm.
Then, for V=?, R= 450, I=20 mA.
V = IR.
= (20*10^-3)*450.
= 9000*10^-3.
v = 9V.
V = IR.
R = V/I.
= 18/40*10^-3.
= (18/40)*10^3.
= 18000/40.
= 450 ohm.
Then, for V=?, R= 450, I=20 mA.
V = IR.
= (20*10^-3)*450.
= 9000*10^-3.
v = 9V.
Raji said:
10 years ago
Current changed but the resistance remains constant. Hence find resistance from given data i.e. v=18V, i=40mA using the formula V=IR.
Now find voltage for new current (20mA) flowing through same resistor using same formula.
Now find voltage for new current (20mA) flowing through same resistor using same formula.
Pravi said:
1 decade ago
First find the resistance,
R = 18/(40*10^-3) = 450.
V' = 450*20*10^-3.
Then, V' = 0.45*20.
V' = 9 v.
R = 18/(40*10^-3) = 450.
V' = 450*20*10^-3.
Then, V' = 0.45*20.
V' = 9 v.
Julea said:
1 decade ago
How did they get 9v?
Darshanmaths said:
1 decade ago
V1 = 18V I1 = 40mA.
V2 = ? I2 = 20mA.
As per ohm's law,
As resistance remains constant.
V1/I1 = V2/I2.
Hence substituting,
18/40 = V2/20.
Hence,
V2=0.45*20 = 9V.
Hence V2 = 9V.
V2 = ? I2 = 20mA.
As per ohm's law,
As resistance remains constant.
V1/I1 = V2/I2.
Hence substituting,
18/40 = V2/20.
Hence,
V2=0.45*20 = 9V.
Hence V2 = 9V.
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