Nuclear reactor moderator function: MCQ with Answer and Explanation

Explanation:
Concave mirror: real, inverted image forms when object beyond focal point (u > f). Between pole and focus: virtual, erect image. At focus: image at infinity. Memory aid: 'Concave: object beyond F ⇒ real image; within F ⇒ virtual'. Ray optics concept frequently tested to verify mirror image formation understanding in competitive exams.

Explanation:
Rectifier (diode bridge) converts AC to DC. Inverter DC to AC. Transformer changes AC voltage level. Oscillator generates AC signal. Electronic devices often need DC.

Explanation:
LEDs are highly efficient, converting ~80-90% of electrical energy into light, rest heat. Incandescent bulbs ~10% efficient. LED long life, low power. Blue LED Nobel prize 2014.