Physics Class 12: Current Electricity & Magnetism

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Questions and Answers

What is the total number of periods allocated for Current Electricity?

25 periods

20 periods

30 periods

22 periods (correct)

Which unit has the highest marks allocated in the syllabus?

Optics (correct)

Magnetic Effects of Current and Magnetism

Electromagnetic Induction and Alternating Currents

Electrostatics

How many chapters are included in the unit on Electrostatics?

1 chapter (correct)

4 chapters

3 chapters

2 chapters

What is the total number of marks for the unit on Electromagnetic Waves?

3 marks Signup and view all the answers

Which chapters are included in the unit on Magnetic Effects of Current and Magnetism?

Moving Charges and Magnetism, Magnetism and Matter Signup and view all the answers

What does Ohm's law relate to in electrical circuits?

The relationship between voltage, current, and resistance Signup and view all the answers

Which of the following describes the concept of mobility in the context of electric current?

The ease with which electric charges move through a material Signup and view all the answers

What is the main principle behind Lenz's Law?

The induced current opposes the change that produces it Signup and view all the answers

What does the term 'reactance' refer to in AC circuits?

The opposition to the flow of alternating current Signup and view all the answers

Which of the following describes the concept of magnetic properties of materials?

Materials can be classified based on their response to magnetic fields Signup and view all the answers

What is the function of a Wheatstone bridge in electrical circuits?

To measure unknown resistances Signup and view all the answers

How does the potential difference relate to electric current?

It determines the flow rate of charge through the circuit Signup and view all the answers

What is a characteristic of a moving coil galvanometer?

It can be converted to an ammeter and voltmeter Signup and view all the answers

What characterizes electromagnetic waves?

They exhibit transverse nature. Signup and view all the answers

Which of the following is a correct application of total internal reflection?

Optical fibers. Signup and view all the answers

According to the photoelectric effect, what happens when light of sufficient frequency is shone on a metal surface?

Electrons are emitted from the surface. Signup and view all the answers

Which formula represents the lensmaker's formula for thin lenses?

$\frac{1}{f} = (n-1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$ Signup and view all the answers

What is the principle behind Young's double slit experiment?

Interference of coherent light waves. Signup and view all the answers

Which equation relates the mass defect to binding energy in nuclear physics?

$E_b = \Delta m \cdot c^2$ Signup and view all the answers

What determines the fringe width in Young's double slit experiment?

Separation between the slits and wavelength of light. Signup and view all the answers

Which of the following best describes the de-Broglie relation?

$\lambda = \frac{h}{mv}$ Signup and view all the answers

What does an intrinsic semiconductor refer to?

A pure semiconductor without any doping. Signup and view all the answers

In a p-n junction diode, what is the primary role of the p-type material?

To create holes for current flow. Signup and view all the answers

Which of the following describes the I-V characteristics of a diode in forward bias?

The current increases exponentially after a certain voltage. Signup and view all the answers

What is the purpose of a potential divider in an electric circuit?

To reduce voltage to desired levels. Signup and view all the answers

Which activity requires measuring the variation in potential drop with length of a wire?

Studying the resistance of a wire. Signup and view all the answers

What type of resistance measurement can be carried out using a meter bridge?

The value of an unknown resistance. Signup and view all the answers

When using a multimeter, which measurement cannot be obtained?

Position of a magnetic field. Signup and view all the answers

In the practical experiment to observe the variation of potential difference across a resistor, which graph will be drawn?

Current vs. potential difference graph. Signup and view all the answers

What method can be used to find the refractive index of a prism?

Measuring the angle of incidence and angle of deviation Signup and view all the answers

Which of the following activities involves identifying a diode using a multimeter?

Identifying a diode, LED, and transistor from a collection Signup and view all the answers

What is the outcome of plotting a sin i – sin r graph for a glass slab?

Determining the refractive index of the material Signup and view all the answers

Which experiment investigates the conservation of energy in a simple pendulum?

Investigating whether the energy of a simple pendulum is conserved Signup and view all the answers

How can the dc forward resistance of a diode be found?

By measuring the forward voltage and current Signup and view all the answers

What is the primary purpose of using two polaroids in an experiment?

To investigate the polarization of light Signup and view all the answers

For a concave lens, which characteristic is true regarding the images formed?

Images are virtual and upright Signup and view all the answers

What is the focus of the project that studies the collision of two balls in two dimensions?

Investigating elastic and inelastic collisions Signup and view all the answers

Study Notes

Current Electricity

Electric current is the flow of electric charges in a metallic conductor.
Drift velocity is the average velocity of charge carriers in a conductor due to an electric field.
Mobility is the ratio of drift velocity to the electric field.
Ohm's law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided the temperature remains constant.
Electrical resistance is the opposition to the flow of current in a conductor.
Resistors can be combined in series or parallel:
- In a series combination, the same current flows through all resistors.
- In a parallel combination, the potential difference across all resistors is the same.
The V-I characteristic of a device shows the relationship between the potential difference across it and the current flowing through it.
Electrical energy is the energy supplied by an electric current.
Electrical power is the rate at which electrical energy is consumed.
Electrical resistivity is a material property that indicates its resistance to current flow.
Electrical conductivity is the reciprocal of resistivity.
The resistance of a conductor increases with temperature.
Internal resistance of a cell is the resistance offered by the electrolyte and the electrodes of the cell.
Electromotive force (emf) of a cell is the maximum potential difference it can produce across its terminals when no current is flowing.
Cells can be combined in series or parallel:
- In a series combination, the emf of the battery is the sum of the emfs of individual cells.
- In a parallel combination, the emf of the battery remains the same as the emf of each individual cell.
Kirchhoff's laws are two fundamental laws used to analyze electrical circuits:
- Kirchhoff's current law (KCL) states that the sum of currents entering a junction is equal to the sum of currents leaving the junction.
- Kirchhoff's voltage law (KVL) states that the sum of potential differences around any closed loop in a circuit must be zero.
A Wheatstone bridge is an electrical circuit used to measure an unknown resistance by comparing it with a known resistance.

Moving Charges and Magnetism

A magnetic field is a region of space where a magnetic force can be experienced.
Oersted's experiment demonstrated that an electric current produces a magnetic field.
Biot-Savart law gives the magnetic field produced by a current element.
Ampere's law relates the line integral of the magnetic field around a closed loop to the current enclosed by the loop.
A solenoid is a long coil of wire that acts like a bar magnet when a current flows through it.
A charged particle moving in a magnetic field experiences a force perpendicular to both its velocity and the magnetic field.
A current-carrying conductor placed in a magnetic field experiences a force proportional to the current, the length of the conductor, and the magnetic field strength.
Two parallel current-carrying conductors exert forces on each other:
- If the currents are flowing in the same direction, the conductors attract each other.
- If the currents are flowing in opposite directions, the conductors repel each other.
The definition of an ampere is based on the force between two parallel current-carrying conductors.
A current loop placed in a uniform magnetic field experiences a torque that tends to align its magnetic dipole moment with the magnetic field.
A moving coil galvanometer is a device used to measure electric current.
The current sensitivity of a galvanometer is a measure of its deflection per unit current.
A galvanometer can be converted into an ammeter or a voltmeter by connecting a suitable resistance in parallel or series with it, respectively.

Magnetism and Matter

A bar magnet is a piece of ferromagnetic material that has a permanent magnetic dipole moment.
A bar magnet can be considered as an equivalent solenoid.
The magnetic field intensity due to a magnetic dipole decreases with distance from the dipole.
A magnetic dipole placed in a uniform magnetic field experiences a torque that tends to align its magnetic dipole moment with the magnetic field.
Magnetic field lines are lines that represent the direction of the magnetic field at each point in space.
Magnetic materials are classified into three categories:
- Paramagnetic materials are weakly attracted to a magnetic field.
- Diamagnetic materials are weakly repelled by a magnetic field.
- Ferromagnetic materials are strongly attracted to a magnetic field.
Magnetization is the process of aligning the magnetic dipoles of a material in a particular direction.

Electromagnetic Induction

Electromagnetic induction is the phenomenon of producing an electromotive force (emf) in a conductor when it is placed in a changing magnetic field.
Faraday's laws of electromagnetic induction state that the emf induced in a conductor is proportional to the rate of change of magnetic flux linked with the conductor.
Lenz's law states that the direction of the induced emf is such as to oppose the change in magnetic flux that produced it.
Self-induction is the phenomenon of producing an emf in a coil due to the changing magnetic field produced by its own current.
Mutual induction is the phenomenon of producing an emf in one coil due to the changing magnetic field produced by the current in a nearby coil.

Alternating Current

Alternating current (AC) is a current that periodically reverses its direction.
The peak value of an AC current is the maximum value of the current.
The RMS value of an AC current is the root-mean-square value of the current, which is equal to the DC current that would produce the same amount of heat in a given resistor.
Reactance is the opposition to the flow of AC current offered by a capacitor or an inductor.
Impedance is the total opposition to the flow of AC current offered by a circuit containing resistors, capacitors, and inductors.
An LCR series circuit is a circuit containing a resistor, an inductor, and a capacitor connected in series.
Resonance is the condition in which the impedance of an LCR series circuit is minimum, and the current is maximum.
Power in an AC circuit is the rate at which electrical energy is consumed.
Power factor is the ratio of the average power to the apparent power in an AC circuit.
Wattles current is the component of current that does not contribute to power consumption.

Electromagnetic Waves

Displacement current is a current that exists in a region of space where an electric field is changing with time.
Electromagnetic waves are transverse waves that consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation.
The transverse nature of electromagnetic waves means that the oscillations of the electric and magnetic fields are perpendicular to the direction of propagation of the wave.
The electromagnetic spectrum is the range of frequencies of electromagnetic waves.
The electromagnetic spectrum includes a wide range of waves, including radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
Each type of electromagnetic radiation has different applications based on its wavelength and frequency.

Ray Optics and Optical Instruments

Ray optics is the study of light based on the concept of light rays.
Reflection of light is the bouncing back of light from a surface.
A spherical mirror is a mirror whose reflecting surface is a portion of a sphere.
The mirror formula relates the object distance (u), the image distance (v), and the focal length (f) of a spherical mirror.
Refraction of light is the bending of light as it passes from one medium to another.
Total internal reflection is the phenomenon of reflection of light from the boundary of two media when the angle of incidence is greater than the critical angle.
Optical fibers are thin, transparent fibers that use total internal reflection to transmit light signals over long distances.
A lens is a transparent medium bounded by two refracting surfaces, of which at least one is curved.
The thin lens formula relates the object distance (u), the image distance (v), and the focal length (f) of a thin lens.
The lens maker's formula relates the focal length of a lens to its radii of curvature and the refractive index of the lens material.
Magnification is the ratio of the size of the image to the size of the object.
The power of a lens is a measure of its ability to converge or diverge light.
A combination of thin lenses in contact can be treated as a single lens whose power is the algebraic sum of the powers of the individual lenses.
A microscope is an optical instrument that uses lenses to magnify small objects.
An astronomical telescope is an optical instrument that uses lenses or mirrors to magnify distant objects.

Wave Optics

Wave optics is the study of light based on the concept of light waves.
A wavefront is a surface that represents all points in space that are in the same phase of vibration.
Huygens' principle states that every point on a wavefront can be considered as a source of secondary wavelets that spread out in all directions with the same speed as the original wave.
The laws of reflection and refraction can be derived using Huygens' principle.
Interference is the phenomenon of superposition of two or more waves, resulting in a new wave pattern with different amplitudes and phases.
Young's double-slit experiment is a classic demonstration of interference of light waves.
Coherent sources are sources that emit waves with a constant phase difference.
Diffraction is the phenomenon of bending of waves around obstacles or through openings.
The width of the central maximum in the diffraction pattern due to a single slit is proportional to the wavelength of light and inversely proportional to the width of the slit.

Dual Nature of Radiation and Matter

The dual nature of radiation means that light exhibits both wave-like and particle-like properties.
The photoelectric effect is the emission of electrons from a metal surface when light shines on it.
Hertz observed that ultraviolet light increases the rate of electron emission in the photoelectric effect.
Lenard observed that the kinetic energy of photoelectrons is independent of the intensity of light.
Einstein's photoelectric equation explains the photoelectric effect by assuming that light consists of packets of energy called photons.
The particle nature of light is supported by experimental findings like the photoelectric effect.
Matter waves are waves associated with moving particles.
De Broglie's relation states that the wavelength of a particle is inversely proportional to its momentum.

Atoms

The alpha-particle scattering experiment conducted by Rutherford provided evidence for the nuclear model of the atom.
Rutherford's model of the atom describes the atom as a positively charged nucleus surrounded by negatively charged electrons.
Bohr's model of the hydrogen atom explains the observed hydrogen spectrum by quantizing the energy levels of the electron.
Bohr's model assumes that electrons revolve around the nucleus in specific orbits with fixed energies.

Nuclei

The nucleus of an atom is the central, positively charged part of the atom.
The nucleus consists of protons and neutrons, which are collectively called nucleons.
The nuclear force is a strong, short-range force that holds the nucleons together in the nucleus.
The mass-energy relation states that mass and energy are equivalent.
Mass defect is the difference in mass between the nucleus and its constituent nucleons.
Binding energy per nucleon is the energy that is required to separate a nucleon from the nucleus.
Nuclear fission is the process of splitting a heavy nucleus into two or more lighter nuclei.
Nuclear fusion is the process of combining two or more light nuclei to form a heavier nucleus.

Semiconductor Electronics: Materials, Devices, and Simple Circuits

Semiconductors are materials that have electrical conductivity between that of conductors and insulators.
Energy bands in solids are ranges of allowed energy levels for electrons.
Conductors have overlapping valence and conduction bands, allowing for easy electron movement.
Insulators have a large energy gap between valence and conduction bands, making electron movement difficult.
Semiconductors have a smaller energy gap than insulators, allowing for some electron movement.
Intrinsic semiconductors are pure semiconductors with an equal number of electrons and holes.
Extrinsic semiconductors are doped with impurity atoms to increase their conductivity.
P-type semiconductors are doped with acceptor impurities, creating an excess of holes.
N-type semiconductors are doped with donor impurities, creating an excess of electrons.
A p-n junction is formed when a p-type semiconductor is joined to an n-type semiconductor.
A semiconductor diode is a device that allows current to flow in one direction only.
The I-V characteristics of a diode show the relationship between the current flowing through the diode and the voltage across it.
A diode can be used as a rectifier to convert AC current to DC current.

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Test your knowledge on the syllabus for the Physics Class 12 curriculum. This quiz covers topics such as Current Electricity, Electrostatics, and Magnetic Effects of Current and Magnetism. Answer questions about periods, marks allocation, and chapters included in these units.