A 12 V battery is connected across an unknown resistor. If a current of 2 mA is flowing through the circuit, the value of the resistance is _________ .
- A.600 ohm
- B.6 ohm
- C.6000 ohm
- D.60 ohm
Correct answer
Explanation
The correct answer is C, 6000 ohm. By Ohm's law the resistance equals the potential difference divided by the current. Here the current must first be converted into the base unit: two milliampere is 0.002 ampere. Dividing twelve volt by 0.002 ampere gives six thousand ohm, that is six kilo-ohm.
Option A, 600 ohm, is what you get if the milliampere is mistaken for a hundredth of an ampere instead of a thousandth, a common slip under time pressure. Option B, 6 ohm, is the answer to a different question, namely twelve volt divided by two ampere, and it ignores the prefix milli altogether. Option D, 60 ohm, does not follow from the numbers at all and is there only to fill the choice. The lesson is to convert every prefix, milli, micro, kilo or mega, into the base unit before dividing.
Read the full article: Electricity and Magnetism: Laws, Rules and PYQs
Practice Questions
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- A.It gets increased
- B.It gets doubled
- C.It gets decreased
- D.It gets halved
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Read the full explanation →What is the work done to move a unit charge from one point to another in an electric circuit carrying some current, between those two points?
- A.Pressure distance
- B.Potential difference
- C.Potential distance
- D.Pressure difference
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The potential difference between two points in a circuit is defined as the work done in moving a unit positive charge from one point to the other.
Read the full explanation →Which of the following is NOT based on the heating effect of current?
- A.Electric heater
- B.Electric bulb (with filament)
- C.Electric iron
- D.Microwave
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Read the full explanation →Thin wires of which of the following metal is used for making the filament of electric bulbs?
- A.Tungsten
- B.Silver
- C.Nichrome
- D.Copper
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Read the full explanation →The direction of the magnetic field produced around a straight current-carrying conductor is given by
- A.Fleming's left hand rule
- B.the right hand thumb rule
- C.Fleming's right hand rule
- D.Lenz's law
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Hold the conductor in your right hand with the thumb stretched along the direction of the conventional current; the way your fingers curl round the wire is the direction of the concentric magnetic field lines.
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