Fleming's left hand rule is used to find the direction of
- A.the induced current in a generator
- B.the force on a current-carrying conductor in a magnetic field
- C.the magnetic field around a solenoid
- D.the potential difference across a resistor
Correct answer
Explanation
The correct answer is B. In Fleming's left hand rule the forefinger, the middle finger and the thumb of the left hand are held at right angles to one another: the forefinger points along the magnetic field, the middle finger along the current, and the thumb then gives the direction of the force. It is the rule behind the electric motor, which converts electrical energy into mechanical energy.
Option A describes Fleming's right hand rule, which is used for the generator, and interchanging the two rules is the single commonest mistake in this chapter. Option C is found instead by the right hand thumb rule applied to each turn of the coil, which shows that a solenoid behaves like a bar magnet. Option D is not a matter of direction in space at all: a potential difference is measured with a voltmeter and needs no hand rule. Remember the pair, left hand for the motor and right hand for the generator.
Read the full article: Electricity and Magnetism: Laws, Rules and PYQs
Practice Questions
View allIf the potential difference across the ends of a conductor is halved, what happens to the current flowing through it?
- A.It gets increased
- B.It gets doubled
- C.It gets decreased
- D.It gets halved
Show answer
By Ohm's law, at a constant temperature the current through a conductor is directly proportional to the potential difference across its ends, since the current equals the potential difference divided by the resistance.
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
Show answer
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
Show answer
A microwave oven does not cook by passing a current through a resistance. It generates microwaves in a magnetron, and these waves make the water molecules in the food rotate rapidly, so the food heats from within by dielectric heating.
Read the full explanation →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
Show answer
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.
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
Show answer
Tungsten has the highest melting point of all metals, well above three thousand degrees Celsius, so a thin tungsten wire can be heated until it glows white without melting.
Read the full explanation →