Electromagnetism MCQs
The magnetic field inside a long, current-carrying solenoid is:
Directly proportional to the radius
Inversely proportional to the number of turns
Nearly uniform and parallel to the axis
Zero at the center
A proton enters a uniform magnetic field perpendicularly. The path of the proton will be a:
Straight line
Circle
Parabola
Helix
The current in a 50 mH inductor changes from 10 A to 2 A in 0.2 seconds. What is the magnitude of the average EMF induced in the inductor?
Lenz's Law is a consequence of the law of conservation of:
The SI unit of magnetic flux is the:
Tesla (T)
Weber (Wb)
Henry (H)
Gauss (G)
A transformer is a device that:
Changes AC voltage
Changes DC voltage
Converts AC to DC
Stores electrical energy
The force on a current-carrying conductor in a magnetic field is maximum when the angle between the conductor and the field is:
0 degrees
45 degrees
90 degrees
180 degrees
An AC generator works on the principle of:
Ohm's Law
Electromagnetic Induction
Heating effect of current
Mutual Induction
The direction of the induced current in a circuit is always such as to oppose the change in magnetic flux that produces it. This is a statement of:
Faraday's Law
Ampere's Law
Lenz's Law
Gauss's Law for Magnetism
What is the charge-to-mass ratio (e/m) for an electron?
1.6 x 10⁻¹⁹ C/kg
9.11 x 10⁻³¹ C/kg
1.76 x 10¹¹ C/kg
6.02 x 10²³ C/kg
In a step-up transformer, the secondary coil has:
Fewer turns than the primary
Equal turns as the primary
More turns than the primary
Zero turns
A galvanometer can be converted into an ammeter by connecting a:
High resistance in series
High resistance in parallel
Low resistance in series
Low resistance in parallel
Motional EMF is induced when a conductor:
Moves through a magnetic field
Is stationary in a changing magnetic field
Is placed in a uniform electric field
Is heated
The energy stored in an inductor is given by the formula:
Magnetic flux will be maximum when the angle between the magnetic field and the area vector is:
0 degrees
45 degrees
90 degrees
180 degrees
In the equation for the magnetic force on a charge, F = qvBsin(θ), θ is the angle between:
Magnetic force and Velocity
Magnetic force and Magnetic field
Velocity and Magnetic field
Electric field and Magnetic field
The phenomenon of producing an EMF in a coil due to a change of current in the same coil is called:
Mutual induction
Self-induction
Electromagnetic induction
Capacitive reactance
A CRO (Cathode Ray Oscilloscope) uses which of the following to deflect the electron beam?
Gravitational fields
Only magnetic fields
Only electric fields
Air pressure
An ideal transformer has 100% efficiency. This means:
Input current equals output current
Input voltage equals output voltage
Input power equals output power
The core has zero permeability
The torque on a current-carrying loop in a magnetic field is maximum when the plane of the loop is:
Parallel to the magnetic field
Perpendicular to the magnetic field
At a 45 degree angle to the magnetic field
Independent of the orientation
Which of the following materials is most suitable for the core of an electromagnet?
Copper
Soft iron
Steel
Aluminum
If the speed of a charged particle moving through a magnetic field is doubled, the magnetic force on it will:
Remain unchanged
Be halved
Be doubled
Be quadrupled
In a velocity selector, a charged particle will pass through undeflected if the electric and magnetic forces cancel. If the electric field is 600 N/C and the magnetic field is 0.02 T, what is the speed of the undeflected particle?
3 x 10³ m/s
1.2 x 10⁴ m/s
3 x 10⁴ m/s
12 m/s
The magnetic field outside an ideal toroid is:
Uniform and strong
Variable
Zero
Half the value inside
According to Faraday's law, the induced EMF is directly proportional to the:
Resistance of the coil
Magnetic flux
Rate of change of magnetic flux
Current in the coil
To convert a galvanometer into a voltmeter, one should connect a:
Low resistance in parallel
Low resistance in series
High resistance in parallel
High resistance in series
Two parallel wires carry current in the same direction. The force between them will be:
Attractive
Repulsive
Zero
Circular
A changing electric flux creates a:
Gravitational field
Magnetic field
Constant electric field
Resistance
The unit Henry (H) can also be expressed as:
Volt / Ampere
Weber / Ampere
Tesla / meter
Coulomb / Volt
Back EMF in a motor is greatest at:
Low speed
High speed
Startup
Constant speed regardless of value
The working principle of a moving coil galvanometer is that a current-carrying coil in a magnetic field experiences:
A linear force
A torque
A change in resistance
An increase in mass
Eddy currents are undesirable in a transformer because they:
Increase the output voltage
Decrease the magnetic flux
Cause energy loss as heat
Magnetize the core permanently
A stationary charge in a magnetic field experiences a force of:
To reduce energy loss due to eddy currents, transformer cores are:
Made from a single solid block
Laminated
Cooled with water
Made from a superconductor
A current of 2 A is flowing in a coil of inductance 5 H. The energy stored in the coil is:
The relationship between the magnetic field B, velocity v, and motional EMF (E) in a conductor of length L is given by:
E = BL/v
E = Bv/L
E = BLv
E = B²Lv
What is the primary cause of the magnetic field of the Earth?
A large permanent magnet in the core
Electric currents in the liquid outer core
Solar wind interacting with the atmosphere
Cosmic rays from outer space
If the number of turns in a solenoid is doubled while keeping the length and current constant, the magnetic field inside will:
Be halved
Remain the same
Be doubled
Be quadrupled
A device that measures very small currents with high sensitivity is the:
Voltmeter
Ammeter
Galvanometer
Ohmmeter
What is the path of an electron projected parallel to a uniform magnetic field?
Circular
Helical
Straight line
Parabolic
A 20 cm long wire carries a current of 10 A and is placed in a 0.4 T magnetic field. If the wire makes an angle of 30° with the field, what is the magnetic force on the wire?
The mutual inductance between two coils depends on their:
Resistance and capacitance
Current and voltage
Geometry and orientation
Temperature and pressure
The magnetic field at the center of a circular current loop is:
Inversely proportional to the current
Directly proportional to the radius
Inversely proportional to the radius
Zero
An ideal step-down transformer decreases:
Current
Voltage
Power
Frequency
The presence of a magnetic field can be detected by a:
Stationary charge
Glass rod
Magnetic compass
Resistor
A proton (mass = 1.67 x 10⁻²⁷ kg, charge = 1.6 x 10⁻¹⁹ C) moves at 2 x 10⁶ m/s and enters a 0.1 T magnetic field at a right angle. What is the radius of its circular path?
For a DC motor, the current drawn is maximum when the motor has:
Just started
Reached maximum speed
A heavy mechanical load
No mechanical load
Ampere's Law is used to calculate:
Electric flux
Magnetic field in symmetric situations
Induced EMF
Resistance
An ideal solenoid has 1000 turns per meter and carries a current of 2 A. What is the magnetic field inside it? (Use µ₀ = 4π x 10⁻⁷ T·m/A)
4π x 10⁻⁴ T
8π x 10⁻⁴ T
2π x 10⁻⁴ T
4π x 10⁻³ T
An electron and a proton enter a magnetic field with the same velocity, perpendicular to the field. They will be deflected:
In the same direction
In opposite directions
With the same radius
They will not be deflected
The purpose of the split-ring commutator in a DC generator is to:
Increase the induced EMF
Reverse current in the external circuit every half rotation
Reverse connection to the external circuit every half rotation
Reduce friction
Start from a north pole and end on a south pole
Form continuous closed loops
Can intersect each other
Are always parallel
A 10 cm wire carrying a current of 5 A is placed in a magnetic field of 0.2 T. If the wire is perpendicular to the field, the force on the wire is:
The strength of the magnetic field is indicated by the:
Length of the field lines
Direction of the field lines
Spacing of the field lines
Color of the field lines
In a region where the magnetic field is zero, a moving charge will experience:
A maximum force
A variable force
No force
A force parallel to its velocity
The direction of the magnetic force on a positive charge is determined by the:
Left-hand rule
Right-hand palm rule
Right-hand grip rule
Ampere's rule
If a current-carrying solenoid is suspended freely, it will align itself in which direction?
East-West
North-South
Vertically
It will not align in any specific direction
The sensitivity of a galvanometer is increased by decreasing the:
Magnetic field strength (B)
Area of the coil (A)
Number of turns (N)
Torsional constant (c) of the suspension wire
A conductor of length 1 m moves at right angles to a magnetic field of 1 T with a velocity of 2 m/s. The induced EMF is:
In a transformer, the primary coil has 100 turns and the secondary has 200 turns. If the input voltage is 120 V AC, the output voltage will be:
Which of the following does NOT affect the magnitude of the induced EMF in a coil?
The rate of change of magnetic flux
The number of turns in the coil
The resistance of the coil
The orientation of the coil in the magnetic field
A 'back current' that opposes the current supplied to a motor is generated by:
The brushes
The commutator
Back EMF
The external load
The unit of self-inductance, the Henry, is equivalent to:
Volt-second per Ampere
Volt-Ampere per second
Ampere-second per Volt
Weber per second
Two parallel wires carry currents in opposite directions. The magnetic field at a point midway between them is:
Zero
Twice the field from one wire
Half the field from one wire
Parallel to the wires
A step-up transformer increases power.
The magnetic domain is a small region in which:
All atoms are aligned magnetically
There are no magnetic atoms
The magnetic fields of atoms cancel each other out
Only north poles are present
What happens to the radius of a charged particle's circular path in a magnetic field if its kinetic energy is doubled?
It is halved
It remains the same
It is doubled
It increases by a factor of sqrt(2)
An ammeter is always connected in ________, and a voltmeter is always connected in ________.
series, parallel
parallel, series
series, series
parallel, parallel
The work done by a magnetic field on a moving charge is always:
Positive
Negative
Zero
Dependent on the charge's mass
An RLC circuit is in resonance. If the inductance L is doubled, what must happen to the capacitance C to maintain resonance?
It must be doubled
It must be halved
It must be quadrupled
It must be quartered
In an AC generator, the induced EMF is maximum when the coil is:
Moving parallel to the magnetic field
Moving perpendicular to the magnetic field
Stationary
At a 45 degree angle to the field
The core of a transformer is laminated to:
Increase the magnetic flux
Reduce energy loss from eddy currents
Make the transformer lighter
Increase the self-inductance of the primary coil
A uniform magnetic field is directed into the page. An electron enters from the top and moves downwards. The force on the electron will be to the:
The time period of a charged particle undergoing circular motion in a uniform magnetic field is independent of its:
Mass
Charge
Magnetic field strength
Velocity
Which device is a practical application of mutual induction?
Generator
Motor
Transformer
Solenoid
If you drop a bar magnet through a vertical copper tube, its acceleration will be:
Equal to g
Less than g
Greater than g
Zero
A galvanometer has a resistance of G and a current Ig gives full-scale deflection. The shunt resistance S required to convert it into an ammeter of range I is:
S = G * Ig / (I - Ig)
S = G * (I - Ig) / Ig
S = G * I / Ig
S = Ig * G / (I + Ig)
The magnetic permeability of free space, μ₀, has a value of:
8.85 x 10⁻¹² C²/Nm²
6.67 x 10⁻¹¹ Nm²/kg²
4π x 10⁻⁷ T·m/A
3.0 x 10⁸ m/s
In a CRT, the purpose of the grid is to:
Accelerate the electrons
Control the brightness of the spot
Deflect the electron beam horizontally
Heat the cathode
If the current in a coil changes from 5 A to 2 A in 0.1 s, inducing an EMF of 3 V, the self-inductance of the coil is:
The main difference between a DC generator and an AC generator is the:
Presence of a magnetic field
Use of a rotating coil
Type of rings used for output
Speed of rotation
A long straight wire carries a current. The magnetic field lines are:
Radial, pointing outwards from the wire
Parallel to the wire
Concentric circles around the wire
Helical around the wire
The torque on a current loop is zero when the angle between the magnetic field and the normal to the plane of the loop is:
0 degrees
45 degrees
90 degrees
270 degrees
A 50 cm long conductor moves at a constant speed of 4 m/s at right angles to a uniform magnetic field of 0.2 T. What is the motional EMF induced in the conductor?
A changing magnetic flux of 1 Wb/s in a coil induces an EMF of 1 V. This is a statement of:
Lenz's Law
Faraday's Law
Ampere's Law
Ohm's Law
If the current through an inductor is doubled, the energy stored in it:
Is halved
Is doubled
Is quadrupled
Remains the same
The operation of a metal detector is based on:
The photoelectric effect
Electromagnetic induction
Static electricity
Capacitance
In a velocity selector, the net force on a charged particle is zero. This means the magnetic force and the electric force are:
In the same direction and equal in magnitude
In opposite directions and equal in magnitude
Perpendicular to each other
Both zero
A transformer cannot work with a DC source because:
DC current has too much power
A DC source produces a constant magnetic flux
The resistance of the primary coil is too high for DC
The iron core cannot be magnetized by DC
The SI unit for magnetic field strength (B) is the Tesla (T). An equivalent unit is:
Newton per (Coulomb-meter)
Newton per (Ampere-meter)
Weber per second
Joule per Ampere
A current-carrying loop is placed in a uniform magnetic field. The net magnetic force on the loop is:
Always zero
Always non-zero
Zero only if the loop is circular
Dependent on the loop's orientation
The final image on the screen of a Cathode Ray Oscilloscope is:
Real and inverted
Virtual and erect
A spot of light
Magnified
An ideal transformer with a primary voltage of 240 V has a secondary voltage of 12 V. If the current in the secondary coil is 2.0 A, what is the current in the primary coil?
The phenomenon where a changing current in one coil induces an EMF in a neighboring coil is called:
Self-induction
Mutual induction
Capacitive coupling
Resistive heating
Increasing the frequency of AC supply to a transformer will:
Decrease the secondary voltage
Increase the secondary voltage
Not change the secondary voltage
Cause the transformer to work on DC
A wire loop is rotated in a uniform magnetic field. The frequency of rotation is doubled. The maximum induced EMF will:
Remain the same
Be halved
Be doubled
Be quadrupled
Paramagnetic materials are weakly:
Attracted to magnetic fields
Repelled by magnetic fields
Unaffected by magnetic fields
Able to become permanent magnets
A charge of 2.0 µC moves at a speed of 3 x 10⁶ m/s perpendicularly through a magnetic field of 0.5 T. What is the magnitude of the magnetic force on the charge?
What is the function of the soft iron core in a moving coil galvanometer?
To increase the resistance of the coil
To make the magnetic field radial and strong
To provide a path for eddy currents
To support the coil and brushes
The power loss in a transformer due to the repeated magnetization and demagnetization of the core is called:
Copper loss
Eddy current loss
Flux leakage
Hysteresis loss
If a magnet is cut into two pieces, what is the result?
Two isolated north poles and two isolated south poles
Two new magnets, each with a north and a south pole
Two non-magnetic pieces
One piece is a north pole and one is a south pole
The magnetic force is strongest when the charged particle moves ________ to the magnetic field lines.
parallel
anti-parallel
perpendicular
at a 45 degree angle
An ideal solenoid is one whose:
length is much larger than its diameter
diameter is much larger than its length
windings are made of a resistive material
core is filled with a diamagnetic material
The output of a DC generator is a:
Steady direct current
Pulsating direct current
Alternating current
Constant voltage
An inductor with an inductance of 80 mH carries a steady current of 5 A. How much energy is stored in its magnetic field?
Two inductors of inductance L₁ and L₂ are connected in series. The total inductance is:
L₁ + L₂
(L₁L₂) / (L₁ + L₂)
sqrt(L₁² + L₂²)
|L₁ - L₂|
The study of charges at rest is called:
Electromagnetism
Electrodynamics
Electrostatics
Magnetostatics
In a mass spectrometer, a charged particle's path radius is proportional to its:
Charge
Mass
Kinetic energy
Magnetic field strength
A flat surface with an area of 0.2 m² is placed in a uniform magnetic field of 0.5 T. What is the magnetic flux through the area if the field is perpendicular to the surface?
Lenz's Law provides the ________ of the induced current.
Magnitude
Direction
Frequency
Power
Other Physics Topics MCQs
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