If an object is placed at the center of curvature of a concave mirror, the image formed is: MCQ with Answer and Explanation

Explanation:
For slabs in series, the rate of heat flow (H) is the same. Total resistance R_eq = R1 + R2. Since thermal resistance R = L / (KA), and total length is 2L: (2L) / (K_eq * A) = (L / K1A) + (L / K2A). Canceling L/A yields 2/K_eq = 1/K1 + 1/K2. Solving gives K_eq = 2K1K2 / (K1 + K2).

Explanation:
A rocket works on the principle of conservation of linear momentum. As the exhaust gases are expelled downward at high velocity, they carry downward momentum. To conserve the total momentum of the system (which is initially zero), the rocket must acquire an equal and opposite (upward) momentum, propelling it forward.

Explanation:
The acceleration due to gravity at a depth 'd' is given by g' = g(1 - d/R), where R is the radius of the Earth. If we go to the center of the Earth, the depth 'd' becomes exactly equal to R. Substituting d = R into the formula gives g' = g(1 - R/R) = g(1 - 1) = 0. So, gravity is zero at the core.