science
1. Who is credited with the discovery that a changing magnetic field produces an electric field?
- André-Marie Ampère
- Heinrich Hertz
- Michael Faraday
- James Clerk Maxwell
Explanation:
- Michael Faraday discovered electromagnetic induction, which is the principle that a changing magnetic flux induces an electromotive force (EMF).
- Ampère worked on the force between current-carrying wires.
- Maxwell unified electricity and magnetism into a single theory.
- Hertz first generated and detected electromagnetic waves.
2. What is the SI unit of magnetic flux?
- Tesla
- Henry
- Weber
- Farad
Explanation:
- Weber (Wb) is the SI unit of magnetic flux.
- Tesla is the unit of magnetic flux density.
- Henry is the unit of inductance.
- Farad is the unit of capacitance.
3. The phenomenon of electromagnetic induction was discovered by which scientist?
- Oersted
- Maxwell
- Lenz
- Faraday
Explanation:
- Michael Faraday discovered electromagnetic induction in 1831.
- Oersted discovered that an electric current creates a magnetic field.
- Maxwell formulated the classical theory of electromagnetism.
- Lenz gave the law defining the direction of the induced current.
4. Which law gives the direction of the induced current in a circuit?
- Faraday’s Law
- Ampere’s Law
- Lenz’s Law
- Coulomb’s Law
Explanation:
- Lenz’s Law states that the direction of the induced current will be such that it opposes the change in magnetic flux that produced it.
- Faraday’s Law gives the magnitude of the induced EMF.
- Ampere’s Law relates the integrated magnetic field around a closed loop to the electric current passing through the loop.
- Coulomb’s Law deals with the force between electric charges.
5. Which of the following is a non-magnetic material?
- Iron
- Nickel
- Cobalt
- Gold
Explanation:
- Gold is diamagnetic, meaning it is weakly repelled by a magnetic field and is considered non-magnetic.
- Iron, Nickel, and Cobalt are ferromagnetic materials, strongly attracted to magnets.
6. What type of transformer is used to increase the voltage?
- Step-down transformer
- Stabilizer
- Converter
- Step-up transformer
Explanation:
- A Step-up transformer has more turns in its secondary coil than in its primary coil, which increases the voltage from primary to secondary.
- A Step-down transformer decreases the voltage.
- A stabilizer maintains a constant voltage level.
- A converter changes the voltage form (e.g., AC to DC).
7. The magnetic field lines inside a current-carrying solenoid are:
- Circular
- Elliptical
- Parallel straight lines
- Radial
Explanation:
- Inside a long solenoid, the magnetic field lines are straight, parallel, and uniformly spaced, indicating a uniform magnetic field.
- The field lines are circular around a straight current-carrying wire.
8. Which rule is used to determine the direction of force on a current-carrying conductor in a magnetic field?
- Right-hand thumb rule
- Maxwell’s cork screw rule
- Fleming’s left-hand rule
- Fleming’s right-hand rule
Explanation:
- Fleming’s left-hand rule is used for motors (force on a conductor).
- Fleming’s right-hand rule is used for generators (direction of induced current).
- The right-hand thumb rule gives the direction of the magnetic field due to a current.
- Maxwell’s corkscrew rule also gives the direction of the magnetic field.
9. The strength of a magnetic field is measured in units of:
- Weber
- Tesla
- Henry
- Ampere
Explanation:
- Tesla (T) is the SI unit of magnetic flux density, which measures the strength of a magnetic field.
- Weber is the unit of magnetic flux.
- Henry is the unit of inductance.
- Ampere is the unit of electric current.
10. What is the main principle behind the working of an electric generator?
- Heating effect of current
- Chemical effect of current
- Electromagnetic induction
- Magnetic effect of current
Explanation:
- An electric generator works on the principle of electromagnetic induction, where mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.
- The heating effect is used in appliances like heaters and irons.
- The chemical effect is used in electroplating and batteries.
- The magnetic effect is used in electromagnets and motors.
11. Which of these materials is used to make a permanent magnet?
- Soft iron
- Steel
- Copper
- Aluminium
Explanation:
- Steel is a hard magnetic material with high retentivity and coercivity, making it suitable for permanent magnets.
- Soft iron has low retentivity and coercivity, so it is used for electromagnets and cores of transformers.
- Copper and Aluminium are non-magnetic materials.
12. The property of a material to retain its magnetism after the magnetizing field is removed is called:
- Coercivity
- Permeability
- Susceptibility
- Retentivity
Explanation:
- Retentivity is the ability of a magnetic material to retain its magnetism after the external magnetizing field is removed.
- Coercivity is the reverse field required to reduce the magnetization to zero.
- Permeability is the measure of a material’s ability to support the formation of a magnetic field within itself.
13. Which device is used to change the voltage of an alternating current (AC)?
- Inverter
- Rectifier
- Generator
- Transformer
Explanation:
- A transformer is a static device that changes AC voltage from one level to another using electromagnetic induction.
- An inverter converts DC to AC.
- A rectifier converts AC to DC.
- A generator converts mechanical energy to electrical energy.
14. Which law describes the force between two stationary electric charges?
- Gauss’s Law
- Ohm’s Law
- Coulomb’s Law
- Biot-Savart Law
Explanation:
- Coulomb’s Law gives the magnitude of the electrostatic force between two point charges.
- Gauss’s Law relates the electric flux through a closed surface to the charge enclosed.
- Ohm’s Law relates current, voltage, and resistance.
- The Biot-Savart Law calculates the magnetic field produced by a current-carrying wire.
15. What is the cause of the Earth’s magnetism?
- Gravitational force
- Magnetic rocks in the crust
- Electric currents in the liquid outer core
- The Sun’s magnetic field
Explanation:
- The widely accepted dynamo theory states that Earth’s magnetism is caused by convective currents in the molten iron-nickel outer core, which acts like a giant electromagnet.
- While crustal rocks have magnetism, they are not the primary cause.
16. Which of the following is NOT an electromagnetic wave?
- Light wave
- X-ray
- Radio wave
- Sound wave
Explanation:
- A sound wave is a mechanical wave that requires a medium (solid, liquid, gas) to travel. It is not an electromagnetic wave.
- Light, X-rays, and Radio waves are all part of the electromagnetic spectrum and can travel through a vacuum.
17. The relative permeability of a ferromagnetic material is:
- Slightly less than 1
- Equal to 1
- Slightly more than 1
- Much greater than 1
Explanation:
- The relative permeability of ferromagnetic materials (like iron) is very high, often in the hundreds or thousands.
- For paramagnetic materials, it is slightly more than 1.
- For diamagnetic materials, it is slightly less than 1.
- For vacuum, it is exactly 1.
18. What is the source of all magnetism?
- Large magnets inside the Earth
- Magnetic monopoles
- The motion of electric charges
- Gravitational forces
Explanation:
- All magnetism arises from the motion of electric charges. This can be the orbital or spin motion of electrons in atoms (microscopic) or an electric current in a wire (macroscopic).
- Magnetic monopoles (single north or south poles) have not been proven to exist.
19. Which effect is utilized in the working of an electric motor?
- Electromagnetic Induction
- Heating Effect
- Magnetic Effect of Electric Current
- Chemical Effect
Explanation:
- An electric motor uses the magnetic effect of electric current. A current-carrying coil experiences a force and rotates when placed in a magnetic field.
- Electromagnetic induction is used in generators.
20. The force between two parallel current-carrying conductors is proportional to:
- The sum of the currents
- The difference of the currents
- The product of the currents
- The square of the currents
Explanation:
- The magnitude of the force per unit length between two parallel wires is F/L = (μ₀ I₁ I₂) / (2π d). It is directly proportional to the product of the currents (I₁ and I₂).
21. What happens to the magnetic field at the center of a circular coil if its radius is doubled and current remains the same?
- Becomes four times
- Becomes two times
- Remains the same
- Becomes half
Explanation:
- The magnetic field at the center is B = (μ₀ I N) / (2 R). It is inversely proportional to the radius (R). So, if the radius is doubled, the field becomes half.
22. Which instrument is used to measure electric current?
- Voltmeter
- Potentiometer
- Galvanometer
- Ohmmeter
Explanation:
- A galvanometer is a device used to detect and measure small electric currents.
- A voltmeter measures potential difference.
- An ohmmeter measures resistance.
- A potentiometer is used to measure an unknown EMF by comparing it with a known EMF.
23. The magnetic susceptibility of a perfect diamagnetic material is:
- Positive and small
- Positive and large
- Negative and small
- -1
Explanation:
- For a perfect diamagnet (like a superconductor), the magnetic susceptibility is χ = -1. This means it perfectly expels an external magnetic field (Meissner effect).
- For paramagnets, it is a small positive number.
- For ferromagnets, it is a large positive number.
24. The core of a transformer is laminated to reduce:
- Hysteresis loss
- Copper loss
- Flux leakage
- Eddy current loss
Explanation:
- Laminating the core with insulated sheets reduces eddy current loss by breaking the path of large circulating currents into smaller, less powerful loops.
- Hysteresis loss is reduced by using soft iron.
25. Which law is a consequence of the conservation of energy in electromagnetic induction?
- Faraday’s Law
- Ampere’s Law
- Lenz’s Law
- Gauss’s Law
Explanation:
- Lenz’s Law is a direct consequence of the conservation of energy. The induced current always opposes the change causing it, meaning work must be done to overcome this opposition, which is the source of the electrical energy generated.