Question 1
What energy transformation takes place in an electric motor?No clue? Show me the answer
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Method #1Direct ApproachStep 1: Identify what an electric motor does
An electric motor is a device that uses electricity to produce motion. We need to identify the correct input and output energy forms.
Step 2: Apply the definition of an electric motor
By definition, an electric motor converts electrical energy (the input — current from a power source) into kinetic (mechanical) energy (the output — rotation of the axle).
Step 3: Select the correct transformation
The correct answer is Electrical energy → Kinetic energy. This is the primary, useful energy transfer in every electric motor, from tiny phone vibrators to large industrial machines.
Method #2Process of EliminationStep 1: Identify what is being asked
The question asks for the energy transformation in an electric motor — specifically, what goes in and what comes out.
Step 2: Eliminate 'Kinetic energy → Electrical energy'
Kinetic → Electrical describes a generator, not a motor. A motor does the opposite — it uses electricity to create motion, not motion to create electricity.
Step 3: Eliminate 'Chemical energy → Thermal energy'
Chemical → Thermal describes a combustion reaction (like burning fuel). An electric motor does not burn anything and does not primarily produce heat as its useful output.
Step 4: Eliminate 'Electrical energy → Chemical energy'
Electrical → Chemical describes a battery being charged, not a motor operating. A motor converts electricity into movement, not into stored chemical energy.
Step 5: Select the correct answer
The only remaining option, Electrical energy → Kinetic energy, correctly describes what an electric motor does — it converts electrical input into mechanical motion output.
Question 2
A student applies Fleming's Left-Hand Rule to find the direction of force on a wire. Which finger represents the direction of the magnetic field?No clue? Show me the answer
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Method #1Direct ApproachStep 1: Recall Fleming's Left-Hand Rule assignments
Fleming's Left-Hand Rule assigns each finger a specific physical quantity. We need to recall which finger corresponds to the magnetic Field.
Step 2: Apply the mnemonic
The mnemonic uses the first letter of each finger's role: First finger = Field, seCond finger = Current, thuMb = Motion. The 'F' in 'First' matches 'Field'.
Step 3: Identify the correct finger
The index finger (first finger) points in the direction of the magnetic field . The middle finger shows current direction and the thumb shows the force (motion) direction.
Method #2Process of EliminationStep 1: Identify what is being asked
We need to identify which specific finger in Fleming's Left-Hand Rule indicates the direction of the magnetic field.
Step 2: Eliminate 'the thumb'
The thumb represents Motion (the force/direction of movement). ThuMb = Motion — so the thumb is not used for the field.
Step 3: Eliminate 'the middle finger (second finger)'
The middle finger represents Current (conventional current direction). SeCond = Current — so the middle finger does not show the field direction.
Step 4: Eliminate 'the ring finger'
The ring finger is not used in Fleming's Left-Hand Rule at all. Only the index finger, middle finger, and thumb are assigned roles.
Step 5: Select the correct answer
By elimination, the index finger (first finger) represents the magnetic Field. This matches the mnemonic: First finger = Field.
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