SET 06

SET 6: NECTA Form Four Physics Conceptual Questions and Answers

121. Explain why pressure decreases as altitude increases.
     Answer: As altitude increases, the density of air decreases because fewer air molecules are present to exert pressure.
     Example: Mountain climbers use oxygen tanks because the air pressure and oxygen level are low at high altitudes.
122. What is the principle of conservation of momentum?
     Answer: The total momentum of a system remains constant if no external forces act on it.
     Example: When two ice skaters push off each other, their momenta are equal and opposite, keeping total momentum constant.
123. Why does a conductor’s resistance increase with temperature?
     Answer: Increasing temperature causes atoms to vibrate more, making it harder for electrons to pass through the conductor.
     Example: Tungsten filaments in bulbs have higher resistance when hot.
124. Explain how sound waves differ from light waves.
     Answer: Sound waves are mechanical and need a medium to travel; light waves are electromagnetic and can travel through vacuum.
     Example: Sound cannot travel in space, but light from the Sun can.
125. Why is the surface tension of water important for small insects?
     Answer: Surface tension allows insects like water striders to walk on water without sinking.
     Example: Water striders use surface tension to stay afloat.
126. What is the function of the anode and cathode in a cathode ray tube?
     Answer: The cathode emits electrons (cathode rays), and the anode accelerates and directs the electrons towards the screen.
     Example: Old TV screens used cathode ray tubes.
127. Describe the process of radioactive decay.
     Answer: Radioactive atoms spontaneously emit particles or energy to become more stable.
     Example: Carbon-14 decays over time and is used in dating archaeological samples.
128. Why do electrical wires have insulating covers?
     Answer: To prevent electric shocks and short circuits by stopping current from escaping the wire.
     Example: Plastic or rubber covers on domestic wiring.
129. Explain why sound travels faster in solids than in gases.
     Answer: Particles in solids are closer together, allowing faster vibration transfer.
     Example: You can hear a train coming by placing your ear on the rail.
130. What causes the blue color of the sky?
     Answer: Scattering of sunlight by air molecules is more effective at shorter (blue) wavelengths.
     Example: The sky appears blue during the day.
131. Define latent heat of vaporization.
     Answer: The amount of heat required to convert a unit mass of liquid into vapor without temperature change.
     Example: Evaporation of water cools the skin.
132. Why does a sharp knife cut better than a blunt one?
     Answer: A sharp knife exerts more pressure on a smaller area, making it easier to cut.
     Example: Sharpened scissors cut fabric better.
133. What is meant by absolute zero?
     Answer: It is the lowest possible temperature (0 K or -273.15°C) where particles have minimum kinetic energy.
     Example: It is theoretical and cannot be reached practically.
134. State the function of a rectifier in electronics.
     Answer: To convert alternating current (AC) to direct current (DC).
     Example: Power adapters use rectifiers to charge batteries.
135. Explain why metals are malleable.
     Answer: The layers of atoms in metals can slide over each other without breaking bonds.
     Example: Copper sheets can be hammered into thin foils.
136. Why is a satellite’s velocity important for orbit?
     Answer: It must be high enough to balance gravitational pull and prevent falling to Earth.
     Example: GPS satellites orbit Earth at specific speeds.
137. What causes the sensation of heat when you touch a hot object?
     Answer: Heat transfer by conduction causes thermal energy to flow into your hand.
     Example: Touching a hot stove causes burning sensation.
138. Define frequency and give its unit.
     Answer: Frequency is the number of waves produced per second, measured in Hertz (Hz).
     Example: The pitch of a musical note depends on frequency.
139. Why does a diver’s body feel heavier underwater?
     Answer: Water exerts an upward buoyant force, but the diver feels heavier due to water pressure on the body.
     Example: Divers use weights to counteract buoyancy.
140. Explain how solar panels generate electricity.
     Answer: Solar cells convert sunlight directly into electrical energy via the photovoltaic effect.
     Example: Solar-powered streetlights.
141. What is meant by the half-life of a radioactive substance?
     Answer: Time taken for half the atoms in a sample to decay.
     Example: Carbon-14’s half-life is about 5730 years.
142. Why do gases exert pressure on the walls of a container?
     Answer: Gas molecules collide with container walls, exerting force per unit area (pressure).
     Example: Inflated tires maintain pressure due to gas molecules inside.
143. State two properties of an ideal gas.
     Answer: (1) Molecules have negligible volume; (2) No intermolecular forces.
     Example: Real gases approximate ideal gas behavior at low pressure.
144. What causes dispersion of light in a prism?
     Answer: Different wavelengths of light refract by different amounts, separating white light into colors.
     Example: Rainbows form due to dispersion.
145. Why does ice float on water?
     Answer: Ice is less dense than liquid water due to its crystalline structure.
     Example: Lakes freeze on top, allowing life beneath.
146. What is inertia?
     Answer: The tendency of an object to resist changes to its state of motion.
     Example: Passengers lurch forward when a car suddenly stops.
147. How does a barometer measure atmospheric pressure?
     Answer: Atmospheric pressure balances the weight of mercury column; height indicates pressure.
     Example: Weather stations use mercury barometers.
148. Why do refrigerators use coolant gases?
     Answer: Coolants absorb heat from inside and release it outside by changing states.
     Example: Freon gas used in many refrigerators.
149. Explain why light travels faster than sound.
     Answer: Light is an electromagnetic wave needing no medium; sound is mechanical and depends on medium density.
     Example: We see lightning before hearing thunder.
150. What causes electric current in a wire?
     Answer: The flow of free electrons through the wire when a potential difference is applied.
     Example: Current flows in a bulb filament when switched on.
151. Define amplitude of a wave.
     Answer: The maximum displacement of a particle from its mean position.
     Example: Higher amplitude sound waves produce louder sounds.