Ultrasound frequencies are typically above MCQ with Answer and Explanation

Explanation:
Thermostat uses differential expansion to make/break circuit.

Explanation:
Resistance decreases with temperature for semiconductors, so α negative.

Explanation:
Potentiometer sensitivity (ability to detect small EMF changes) increases with longer wire because potential gradient (V/cm) decreases, allowing finer measurement of balancing length. Sensitivity ∝ length of wire. Decreasing length (B) reduces sensitivity; increasing current (C) increases potential gradient, reducing sensitivity; thicker wire (D) reduces resistance but doesn't directly affect sensitivity if current adjusted. Memory tip: 'Longer potentiometer wire ⇒ smaller potential gradient ⇒ higher sensitivity'. This experimental physics concept is frequently tested in competitive exams. Always link sensitivity to potential gradient: smaller gradient allows detection of smaller voltage differences.