Physics 2016 Jamb Examination

Boiling is the rapid phase transition from liquid to gas that occurs throughout the bulk of the liquid. Unlike evaporation, which happens only at the surface, boiling occurs when the temperature of the liquid is high enough that its saturated vapour pressure becomes equal to the external atmospheric pressure. At this point, bubbles of vapour can form within the liquid and rise to the surface.

Magnification \( m \) is given by \( m = \frac{v}{u} \). For a virtual image in a convex lens, \( v \) is negative according to the real-is-positive convention.
Given:
\( u = 10 \text{ cm} \)
\( m = 3 \)
Therefore, \( v = - (m \times u) = - (3 \times 10) = -30 \text{ cm} \).
Using the lens formula:\[ \frac{1}{f} = \frac{1}{u} + \frac{1}{v} \]\[ \frac{1}{f} = \frac{1}{10} + \frac{1}{-30} \]\[ \frac{1}{f} = \frac{3 - 1}{30} = \frac{2}{30} \]\[ f = \frac{30}{2} = 15 \text{ cm} \]

In a velocity-time (v-t) graph, acceleration is represented by the gradient (slope) of the line. For a body starting from rest, the graph must pass through the origin \( (0,0) \). 'Uniform acceleration' means the velocity increases at a constant rate, which results in a straight line with a constant positive slope. Graph B represents this motion. 

A neutral point in a magnetic field is a point where the resultant magnetic flux density is zero. This occurs when two magnetic fields (e.g., from two magnets or a magnet and the Earth's field) are equal in magnitude but opposite in direction. In the provided diagram showing two like poles (e.g., North and North) facing each other, the magnetic field lines repel each other, leaving a space in the center labeled 'X' where no field lines pass. This is the neutral point.

To read a micrometer screw gauge:
1. Main Scale Reading: The sleeve shows 4.0mm (4 whole millimeters).
2. Thimble Scale Reading: The 16th mark on the thimble aligns with the datum line on the sleeve. Since each division on the thimble represents 0.01mm, this is \( 16 \times 0.01 = 0.16 \text{ mm} \).
3. Total Reading: \( 4.0 \text{ mm} + 0.16 \text{ mm} = 4.16 \text{ mm} \).

Magnetic field lines are defined to emerge from the North pole (N) and enter the South pole (S). In the space between two opposite poles, the magnetic field is directed from N to S. Because opposite poles attract each other, the force experienced by the North pole will be towards the South pole, and vice versa. Therefore, the direction of the force/field between the poles is from North to South (NS).

According to modern atomic theory and Dalton's fundamental postulates, atoms of different elements differ in their properties, including their mass and chemical behavior. Statement D is false because if all atoms were identical, there would be only one type of element in the universe. In reality, the number of protons in the nucleus (atomic number) identifies the element and makes its atoms unique compared to atoms of other elements.

Beats are a phenomenon caused by the interference of two sound waves of slightly different frequencies. The beat frequency (\( f_b \)) is simply the absolute difference between the frequencies of the two sources:\[ f_b = |f_2 - f_1| \]Given:
\( f_1 = 258 \text{ Hz} \)
\( f_2 = 270 \text{ Hz} \)
Calculation:\[ f_b = 270 - 258 = 12 \text{ Hz} \]The listener will hear the volume of the sound pulse or 'beat' 12 times per second.