NEB Class 12 • Physics • Electricity and Magnetism • Practice Set

Alternating Current Practice Set: NEB 12 Physics

Master Alternating Current through physical meaning, diagrams, a reliable answer method and exam-focused practice.

ConceptsWorked reasoningNEB practice

Worked practice

Build the result from meaning, not memory

Alternating voltage and current vary periodically. Resistance dissipates energy; inductance and capacitance store and return energy, producing phase differences and frequency-dependent reactance.

Worked example

A sinusoidal 325 V peak supply has about 230 V rms. For a pure resistor, average power is VrmsIrms.

The governing relationship is Vrms=V0/√2, Irms=I0/√2, XL=ωL, XC=1/(ωC), and series RLC impedance Z=√(R²+(XL−XC)²). Check the convention, geometry or boundary condition before calculation.

Independent practice ladder

Define the key physical quantities and give their SI units.
Draw and label the relevant wave, ray, mode or energy diagram.
Recalculate the worked example after changing one input by a factor of two.
Explain the result without equations.
Create a Nepal-relevant situation such as a classroom speaker, musical pipe, optical slit or thermal machine.
Compare two cases and predict the larger output before calculating.
Find and repair one deliberately wrong sign, node or unit.
Write a three-mark answer and a five-mark answer.

Answer protocol: diagram → known data → principle → symbolic equation → SI substitution → result → physical check. Using peak values in an rms power equation, adding reactances without signs, or claiming an ideal inductor consumes average power.

NEB answer method

Diagram → principle → equation → check

First identify the physical system and what the question asks. Label the diagram with SI quantities, then write the principle in words before selecting a formula. Solve symbolically where possible and check dimensions, limiting cases and direction.

Stage	Question to ask	Evidence in answer
Model	What is idealised?	Boundary or assumption stated
Representation	Which diagram fits?	Labels, nodes, rays or energy arrows
Calculation	Which relation follows?	Symbols then SI values
Evaluation	Does it make sense?	Unit, sign and trend check

Make the idea concrete in Nepal

Connect the model to a school laboratory, musical instrument, auditorium, mobile communication, optical instrument or energy device. The example should clarify the physics rather than merely mention a place. For a visual experiment, use PhET Wave Interference and record which variable you changed and what observation followed.

Review the Class 12 Physics revision roadmap and the complete Physics guide. For online or physical tuition, call 9846662070.

Frequently asked questions

Questions students ask about Alternating Current

What is the central idea of Alternating Current?+

Alternating voltage and current vary periodically. Resistance dissipates energy; inductance and capacitance store and return energy, producing phase differences and frequency-dependent reactance.

Which equation should I remember?+

Vrms=V0/√2, Irms=I0/√2, XL=ωL, XC=1/(ωC), and series RLC impedance Z=√(R²+(XL−XC)²).

How should I begin a numerical?+

Draw the situation, list known quantities in SI units, choose the governing relation symbolically, substitute once and finish with a unit and reasonableness check.

What is a common exam mistake?+

Using peak values in an rms power equation, adding reactances without signs, or claiming an ideal inductor consumes average power.

How can I practise this topic?+

Alternate one concept explanation, one diagram and two numericals. Revisit errors after a day instead of only rereading the solution.

Where can I get tuition support?+

For online or physical KTM Tuition classes, call 9846662070. After Grade 12, the MKS Education panel below gives preparation and pre-counselling contacts.

References and next steps

Scope checked against CDC Nepal; concept support from OpenStax and PhET. Continue with the Alternating Current cluster.

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