When ray of light incident normally on a plane mirror, then incident angle = 0°.
∴ Reflection angle also be 0° [according to the 2nd law of reflection of light].
Again, we know that in that case direction of incident ray and reflected ray are opposite to each other.
Hence, the required angle must be 180°.

Convex mirror because a mirror is diverging in nature. Light rays incident at its extreme corners gets diverged following laws of reflection. Hence if we draw the diagram we can clearly understand that the reflected rays follow a wider path. While in case of a plane mirror the divergence is not so large.

Size of the image must be same as the object size if an object is placed perpendicular to the principal axis of a concave mirror at a distance equal to 2f or r (radius of curvature).

No explanation

For semiconductor, resistance decreases with increases the temperature.

Work-done in moving a electrical charge, W = Potential difference (V) × amount of charge (Q) ⇒ 10 × 4 Joules = 40 J

No explanation.

According to the question, both the batteries are connected in opposite direction.
Thus, total voltage = (24 − 10) V ⇒ 14 V

4Ω and 2Ω are connected in series [see figure].
∴ Equivalent resistance of 4Ω and 2Ω resistances = (4 + 2)Ω ⇒ 6Ω.
Again 6Ω and 3Ω resistances are connected in parallel combination.
Thus, the required equivalent resistance between A and B =

6×36+3=2 Ω

By the definition of average speed, we have
Average speed =

total distance  total time⇒

circumference of circular track  total time⇒

2×3.14×100  62.8ms⁻¹ = 10 ms⁻¹