Assertion (A): In a purely resistive AC circuit, voltage and current are in phase. Reason (R): Resistors do not store energy; they dissipate it as heat. MCQ with Answer and Explanation
Question
Report Error
Discuss this Question (0)
Practice More Physics Questions
Question #1
Report Error
The focal length of a concave mirror is 20 cm. An object is placed at 30 cm from the mirror. The image distance is:
Correct Answer: Option C
Explanation:
Mirror formula: 1/f = 1/u + 1/v. Sign convention: f negative for concave mirror? Wait, standard Cartesian: f = -20 cm (concave), u = -30 cm (object real). Thus 1/(-20) = 1/(-30) + 1/v ⇒ -1/20 = -1/30 + 1/v ⇒ 1/v = -1/20 + 1/30 = (-3+2)/60 = -1/60 ⇒ v = -60 cm. Magnitude 60 cm, negative sign indicates real image in front of mirror. Many exams use magnitude-only options; here 60 cm is correct. Memory tip: 'Concave mirror: object beyond C (2f) ⇒ image between F and C, real, inverted'. This numerical tests mirror formula application with sign conventions, crucial for optics in competitive exams.
Mirror formula: 1/f = 1/u + 1/v. Sign convention: f negative for concave mirror? Wait, standard Cartesian: f = -20 cm (concave), u = -30 cm (object real). Thus 1/(-20) = 1/(-30) + 1/v ⇒ -1/20 = -1/30 + 1/v ⇒ 1/v = -1/20 + 1/30 = (-3+2)/60 = -1/60 ⇒ v = -60 cm. Magnitude 60 cm, negative sign indicates real image in front of mirror. Many exams use magnitude-only options; here 60 cm is correct. Memory tip: 'Concave mirror: object beyond C (2f) ⇒ image between F and C, real, inverted'. This numerical tests mirror formula application with sign conventions, crucial for optics in competitive exams.
Question #2
Report Error
Electric motor works on principle of:
Correct Answer: Option A
Explanation:
Motor: current-carrying conductor in magnetic field experiences Lorentz force (F = ILB), causing rotation. Generator uses reverse principle (induction). Memory tip: 'Motor: electricity ⇒ motion (force); Generator: motion ⇒ electricity (induction)'. Device principle question frequently tested in competitive electromagnetism sections.
Motor: current-carrying conductor in magnetic field experiences Lorentz force (F = ILB), causing rotation. Generator uses reverse principle (induction). Memory tip: 'Motor: electricity ⇒ motion (force); Generator: motion ⇒ electricity (induction)'. Device principle question frequently tested in competitive electromagnetism sections.
Question #3
Report Error
When a body falls freely under gravity, which statement is correct?
Correct Answer: Option C
Explanation:
In free fall under gravity alone, mechanical energy (kinetic + potential) is conserved, assuming no air resistance. Potential energy decreases while kinetic energy increases, sum constant. Law of conservation of mechanical energy. Non-conservative forces absent.
In free fall under gravity alone, mechanical energy (kinetic + potential) is conserved, assuming no air resistance. Potential energy decreases while kinetic energy increases, sum constant. Law of conservation of mechanical energy. Non-conservative forces absent.
No comments yet. Be the first to start the discussion!