For Class 8, 9 & 10
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Showing 6 questions in Physics for Class 8. Tap a card to reveal the answer.
PhysicsForce and PressureeasyA sharp knife cuts better than a blunt one. Explain using the idea of pressure.
Reveal answer ↓
What it is
Pressure is how concentrated a force is - the same push on a smaller area presses much harder.
Answer
Pressure is the force acting on a unit area, P = F/A. A sharp knife has a very small area at its edge, so for the same force the pressure it exerts is much greater, and it cuts easily. A blunt knife has a larger edge area, so the same force produces less pressure and cuts poorly.
P = F / A
- •Pressure = force / area (P = F/A)
- •Smaller area -> greater pressure
- •Sharp edge = small area = high pressure
Why learn this
It explains sharp knives, nails, a camel's wide feet on sand, and why a thin bag strap hurts your shoulder.
💡 Memory trick
Same force, Smaller area = Stronger press - the three S's.
PhysicsFrictionmediumWhy is friction called a necessary evil?
Reveal answer ↓
What it is
Friction is the grip between two surfaces that resists sliding.
Answer
Friction is called a necessary evil because it is both useful and harmful. It is necessary as it lets us walk, hold objects, write and stop vehicles. It is an evil because it wears out machine parts and shoe soles and produces heat that wastes energy. So we increase it where needed (treads, brakes) and reduce it where it wastes energy (lubricants, ball bearings).
- •Useful: walking, gripping, braking, writing
- •Harmful: wear and tear, heat, energy loss
- •Increase with treads/brakes; reduce with lubricants/ball bearings
Why learn this
Without it you couldn't walk, write or brake; too much of it wastes fuel and wears parts out.
💡 Memory trick
Friction is a Friend that also causes Fiction (trouble).
PhysicsSoundeasyHow is sound produced, and why can it not travel through vacuum?
Reveal answer ↓
What it is
Sound is a vibration that travels by shaking the particles of a medium.
Answer
Sound is produced by vibrating objects; the vibrations push the particles of the surrounding medium, creating compressions and rarefactions that travel outward as a wave. Sound needs a material medium (solid, liquid or gas) because it moves by making particles vibrate. In a vacuum there are no particles, so sound cannot travel.
- •Produced by vibration
- •Travels as compressions and rarefactions
- •Needs a material medium
- •Cannot travel in vacuum (no particles)
Why learn this
It's why space is silent for astronauts and why you hear an approaching train through the rails first.
💡 Memory trick
No particles, no sound - a vacuum means silence.
PhysicsChemical Effects of Electric CurrentmediumWhat is electroplating? Give one use of it.
Reveal answer ↓
What it is
Electroplating uses electricity to coat one metal with a thin layer of another.
Answer
Electroplating is the process of depositing a layer of one metal over another using electricity (the chemical effect of electric current). When current passes through a solution of a metal salt, metal ions are deposited on the object connected to the negative terminal. It is used to coat iron with chromium or nickel to prevent rusting and to make cheap ornaments look like gold or silver.
- •Depositing one metal over another using electricity
- •Uses the chemical effect of current
- •Object at negative terminal gets coated
- •Used to prevent rusting and for jewellery
Why learn this
It stops rusting (chrome on bikes and taps) and makes cheap jewellery look like gold or silver.
💡 Memory trick
Electro-PLATE = electricity lays a PLATE of metal on top.
PhysicsLighteasyState the two laws of reflection of light.
Reveal answer ↓
What it is
Reflection is light bouncing off a surface following two fixed rules.
Answer
First law: the incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane. Second law: the angle of incidence is always equal to the angle of reflection (i = r).
angle i = angle r
- •Incident ray, reflected ray and normal lie in one plane
- •Angle of incidence = angle of reflection (i = r)
- •Angles are measured from the normal, not the surface
Why learn this
It's why mirrors, periscopes and even your reflection in still water work.
💡 Memory trick
Angle IN equals angle OUT (i = r), both measured from the normal.
PhysicsSome Natural PhenomenamediumWhat causes lightning, and how does a lightning conductor protect a building?
Reveal answer ↓
What it is
Lightning is a huge electric spark between charged clouds or between a cloud and the ground.
Answer
During a thunderstorm, air currents make the top of a cloud positively charged and the bottom negatively charged. When the charge grows large enough it jumps as a giant spark - lightning - to another cloud or to the ground. A lightning conductor is a metal rod fixed at the top of a building and connected to the earth; it safely carries the lightning's charge into the ground and protects the building.
- •Charge separation in storm clouds
- •Large charge jumps as a spark (lightning)
- •Lightning conductor carries charge safely to earth
Why learn this
It explains thunderstorms and why tall buildings need protection - real safety science.
💡 Memory trick
Charges build up, then jump as a spark. A lightning conductor gives them a safe path to the ground.