Basic Concepts of Physics
Basic Concepts of Physics
General Science is one of the five equal parts of the 40-question Part-II paper, so expect about 8 science questions in all, of which physics supplies roughly 3. They are definition and unit based, drawn from class 6 to 8 material, and they reward clean recall rather than calculation.
Motion and Force
Distance is the total path covered and is always positive. Displacement is the shortest straight line from start to finish and can be zero. A student walking once around a school field covers distance but ends with zero displacement.
Newton's three laws are the most asked block in physics.
- A body stays at rest or in uniform motion unless an external force acts — the law of inertia.
- Force equals mass times acceleration, so F = ma.
- Every action has an equal and opposite reaction.
F = m × a | Momentum p = m × v
A passenger lurching forward when a bus brakes suddenly is the standard example of the first law, and it appears in papers as often as the law itself.
Work, Energy and Power
Work = Force × Displacement | Power = Work ÷ Time
Work is done only when the body actually moves in the direction of the force. Pushing hard against a wall that does not move means zero work in the scientific sense. Energy is neither created nor destroyed, only converted — that is the law of conservation of energy.
✗ Holding a heavy bag steady does work | ✓ No displacement means no work is done
Light and Sound
Light travels in straight lines and reflects off mirrors. A concave mirror can form a real or virtual image and is used in headlights and shaving mirrors; a convex mirror always forms a small virtual image and is used as a rear-view mirror because it gives a wider field of view.
For vision defects, myopia or short-sightedness is corrected by a concave lens, and hypermetropia or long-sightedness by a convex lens.
Sound needs a material medium and cannot travel through a vacuum. The audible range for a healthy human ear is roughly 20 Hz to 20,000 Hz; above that is ultrasound.
✗ Sound travels through vacuum, light does not | ✓ Light travels through vacuum, sound does not
Electricity and Units
Ohm's law: V = I × R
| Quantity | SI Unit | Measured by |
|---|---|---|
| Force | Newton | — |
| Work / Energy | Joule | — |
| Power | Watt | — |
| Current | Ampere | Ammeter |
| Potential difference | Volt | Voltmeter |
| Resistance | Ohm | — |
| Frequency | Hertz | — |
कार्य तभी होता है जब वस्तु बल की दिशा में हटे — सिर्फ जोर लगाने से कार्य नहीं होता।
TRE pointer: Since you are being selected to teach classes 6 to 8, the examiner keeps physics at NCERT level and tests whether you can state a law cleanly, not solve it. The most repeated trap is the light-and-sound swap: sound needs a medium, light does not. Remember the marking rule as well — five options A to E, −1/3 for a wrong answer, and option E must be marked if you want to skip, because a blank row is penalised the same way.
60-Second Recap
- Distance is the path covered; displacement is the shortest line and can be zero.
- Newton's first law is inertia; second gives F = ma; third is action-reaction.
- Work needs displacement — no movement means no work.
- Concave mirror for headlights, convex for rear-view; concave lens corrects myopia.
- Sound needs a medium and cannot travel in vacuum; audible range 20 Hz to 20,000 Hz.
- Learn the unit table: newton, joule, watt, ampere, volt, ohm, hertz.
Frequently Asked Questions
Can sound travel through a vacuum?
No. Sound is a mechanical wave and needs a material medium such as solid, liquid or gas to travel through. Light, being an electromagnetic wave, does not need a medium and travels through vacuum. Questions frequently reverse this pair, so store the two facts together as a contrast.
Which mirror is used in vehicle rear-view mirrors and why?
A convex mirror. It always produces a small, erect, virtual image and covers a much wider field of view than a plane mirror of the same size, letting the driver see more of the road behind. Concave mirrors, by contrast, are used in headlights and shaving mirrors.
What is the difference between distance and displacement?
Distance is the total length of the path actually travelled and is always positive. Displacement is the straight-line gap between the starting and finishing points, with direction. If a body returns to where it began, the distance is large but the displacement is exactly zero.
How many physics questions come in BPSC TRE Part-II?
General Science contributes roughly eight of the forty Part-II questions and physics accounts for about three of them. They stay at class 6 to 8 level and focus on definitions, laws, units and everyday applications rather than numerical problem solving.