CBSE 2025 · Region 7 · Set 1 · Q25 · 3 marks
(a)Differentiate between 'conduction current' and 'displacement current', giving one similarity and one dissimilarity between them.(b)Explain the existence of electromagnetic waves in free space, using the concept of displacement current.
(a)
Differentiate between 'conduction current' and 'displacement current', giving one similarity and one dissimilarity between them.
(b)
Explain the existence of electromagnetic waves in free space, using the concept of displacement current.
Marking-scheme solution
(a)
Similarity
Both give rise to magnetic field.
Dissimilarity
Conduction current is due to flow of charges in the conductor.
Displacement current arises due to change in electric field/ time varying electric flux.
(b)
A magnetic field, changing with time, gives rise to an electric field. Then, an electric field changing with time gives rise to a magnetic field and is a consequence of the displacement current being a source of a magnetic field. Thus, time-dependent electric and magnetic fields give rise to each other and hence em wave is generated.
$$\oint \vec{B}\cdot\vec{dl} = \mu_0 I_c + \mu_0 \varepsilon_0 \frac{d\Phi_e}{dt}$$
Electromagnetic WavesDisplacement CurrentUnderstandshort_answermedium
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CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.