CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Transformers
A step-down transformer does what to voltage?
A. Converts AC to DC directly
B. Increases it
C. Decreases it
D. Always doubles frequency
Correct Answer: C
A step-down transformer has fewer secondary turns than primary turns.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Transformers
A step-up transformer does what to voltage?
A. Increases it
B. Keeps it at zero
C. Decreases it
D. Converts it to heat only
Correct Answer: A
A step-up transformer has more turns on the secondary than the primary.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Transformers
What is the main function of a transformer?
A. Convert DC directly without switching
B. Change AC voltage and current levels by electromagnetic induction
C. Store chemical energy
D. Measure temperature
Correct Answer: B
Transformers transfer AC power between coils through a changing magnetic flux.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Resistance
For most metals, resistance usually does what as temperature rises?
A. Decreases to zero in all cases
B. Becomes negative
C. Increases
D. Never changes
Correct Answer: C
Lattice vibrations increase with temperature, impeding electron flow.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Resistance
What material property appears in R = ρL/A?
A. Magnetic field only
B. Resistivity
C. Density only
D. Capacitance
Correct Answer: B
Resistivity ρ characterizes how strongly a material resists current.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Resistance
For a uniform wire, increasing cross-sectional area generally does what to resistance?
A. Makes it infinite
B. Has no effect
C. Increases it
D. Decreases it
Correct Answer: D
R = ρL/A, so larger area reduces resistance.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Resistance
For a uniform wire, increasing its length generally does what to resistance?
A. Has no effect
B. Increases it
C. Decreases it to zero
D. Makes resistance negative
Correct Answer: B
For fixed material and area, R is proportional to length.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Resistance
What is the SI unit of resistance?
A. Ampere
B. Watt
C. Ohm
D. Volt
Correct Answer: C
The ohm is the SI derived unit of resistance.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Resistance
What is electrical resistance?
A. Rate of charge flow
B. Magnetic flux only
C. Opposition a material offers to electric current
D. Energy per unit charge
Correct Answer: C
Resistance quantifies how strongly a component opposes current.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Ohm's Law
Which SI unit measures resistance?
A. Coulomb
B. Ampere
C. Volt
D. Ohm
Correct Answer: D
Resistance is measured in ohms, symbol Ω.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Ohm's Law
If voltage stays constant and resistance doubles, current does what?
A. Doubles
B. Stays exactly the same
C. Halves
D. Becomes zero always
Correct Answer: C
From I = V/R, doubling R halves I.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Ohm's Law
If I = 2 A and R = 5 Ω, what voltage is required?
A. 7 V
B. 0.4 V
C. 2.5 V
D. 10 V
Correct Answer: D
Using V = IR gives 2×5 = 10 V.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Ohm's Law
If V = 12 V and R = 4 Ω, what current flows?
A. 0.33 A
B. 8 A
C. 3 A
D. 48 A
Correct Answer: C
Using I = V/R gives 12/4 = 3 A.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Ohm's Law
Which equation represents Ohm's law?
A. F = ma
B. V = IR
C. P = VI only
D. Q = It only
Correct Answer: B
Ohm's law relates potential difference, current and resistance.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Ohm's Law
What does Ohm's law state for an ohmic conductor at constant physical conditions?
A. Resistance is always zero
B. Current is proportional to resistance
C. Voltage is proportional to current
D. Power is independent of voltage
Correct Answer: C
For an ohmic conductor, V = IR.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Motors
Which device performs the reverse energy conversion of a motor?
A. Resistor
B. Generator
C. Transformer only
D. Thermometer
Correct Answer: B
A generator converts mechanical energy into electrical energy.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Motors
What component supplies magnetic field in a simple motor?
A. Permanent magnets or electromagnets
B. Fuse only
C. Ammeter only
D. Capacitor only
Correct Answer: A
The stator field interacts with current in the armature or rotor.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Motors
What is the function of a commutator in a simple DC motor?
A. Cool the motor
B. Increase resistance only
C. Store charge permanently
D. Reverse coil current every half-turn to maintain torque direction
Correct Answer: D
The split-ring commutator reverses current so rotation continues in the same sense.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Motors
What does Fleming's left-hand rule determine?
A. Direction of heat flow
B. Direction of gravity
C. Direction of induced current in a generator
D. Direction of force in a motor
Correct Answer: D
The left-hand rule gives the relationship among field, current and force in motor action.
CSS - PMS - CCE - PCS - General Science
Electricity & Magnetism - Motors
What force principle allows a current-carrying conductor in a magnetic field to move?
A. Magnetic force on current
B. Nuclear force
C. Buoyant force
D. Surface tension
Correct Answer: A
A conductor carrying current experiences force in an external magnetic field.