SET 07

SET 7: NECTA Form Four Physics Conceptual Questions and Answers

151. What is meant by electric potential?
     Answer: Electric potential at a point is the work done to move a unit positive charge from infinity to that point.
     Example: A battery creates a potential difference that pushes charges in a circuit.
152. Explain why sound cannot travel in a vacuum.
     Answer: Sound is a mechanical wave that requires a medium (solid, liquid or gas) to propagate. In a vacuum, there are no particles to vibrate.
     Example: No sound is heard in space.
153. Describe the photoelectric effect.
     Answer: When light of certain frequency hits a metal surface, it ejects electrons from the surface.
     Example: Solar cells convert light energy into electrical energy via the photoelectric effect.
154. Why do astronauts appear weightless in orbit?
     Answer: They are in free fall around the Earth, so both astronauts and spacecraft accelerate equally, creating a sensation of weightlessness.
     Example: International Space Station astronauts float inside the station.
155. What is meant by frequency modulation (FM)?
     Answer: FM is a method of encoding information by varying the frequency of a carrier wave.
     Example: FM radio stations transmit high-quality sound signals.
156. Why is the filament of an electric bulb made of tungsten?
     Answer: Tungsten has a very high melting point and emits light efficiently when heated.
     Example: Filaments glow without melting easily.
157. Explain why a car safety belt reduces injury during a collision.
     Answer: It increases the time over which the body’s momentum changes, reducing the force experienced.
     Example: Wearing seat belts reduces risk of injury.
158. State Snell’s Law.
     Answer: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for two given media.
     Example: Light bending when entering water from air.
159. Why do metal objects feel colder than wooden objects at room temperature?
     Answer: Metals conduct heat away from your skin faster than wood, making them feel colder.
     Example: A metal door handle feels cold compared to a wooden door.
160. What is meant by efficiency of a machine?
     Answer: Efficiency is the ratio of useful work output to total work input, expressed as a percentage.
     Example: A car engine with 30% efficiency converts 30% of fuel energy into useful work.
161. Why do planets revolve around the sun?
     Answer: Due to the gravitational force exerted by the Sun providing centripetal force keeping planets in orbit.
     Example: Earth’s orbit around the Sun.
162. Define wavefront.
     Answer: A wavefront is a surface over which all points have the same phase of vibration.
     Example: Circular ripples spreading on water surface.
163. Explain how a liquid thermometer works.
     Answer: The liquid expands or contracts with temperature changes, causing the level in the tube to rise or fall.
     Example: Mercury thermometer shows temperature by mercury column height.
164. What causes tides on Earth?
     Answer: Tides are caused by the gravitational pull of the Moon and Sun on Earth’s oceans.
     Example: High tide during full moon and new moon.
165. Why is neon used in advertising signs?
     Answer: Neon gas emits bright light when electricity passes through it.
     Example: Neon lights glowing red in shop signs.
166. What is the function of the commutator in a DC motor?
     Answer: It reverses the direction of current to keep the motor rotating continuously.
     Example: Used in electric drills.
167. Explain why ice melts faster on metal than on plastic.
     Answer: Metal conducts heat better than plastic, transferring heat faster to the ice.
     Example: Ice on a metal plate melts before ice on a wooden table.
168. What is the difference between longitudinal and transverse waves?
     Answer: Longitudinal waves have particle vibration parallel to wave direction; transverse waves have vibrations perpendicular.
     Example: Sound waves are longitudinal; light waves are transverse.
169. Why is the boiling point of water lower at high altitudes?
     Answer: Atmospheric pressure is lower at high altitudes, so water boils at a lower temperature.
     Example: Cooking times are longer in highland areas.
170. Describe how electric bell works.
     Answer: Electric current magnetizes the electromagnet which attracts the hammer to strike the gong, breaking the circuit and causing the hammer to return.
     Example: Doorbells use this principle.
171. State one use of a convex lens.
     Answer: Used in magnifying glasses to enlarge small objects.
     Example: Used by jewelers to examine details.
172. Explain why vacuum cleaners work better when sealed properly.
     Answer: A good seal creates strong suction by preventing air leaks.
     Example: Vacuum cleaners lose efficiency if the hose is broken.
173. What causes the blue color of the ocean?
     Answer: Water absorbs longer wavelengths (red) and scatters shorter blue wavelengths.
     Example: Tropical oceans appear deep blue.
174. Why do gases expand when heated?
     Answer: Increased kinetic energy makes molecules move faster and occupy more space.
     Example: Hot air balloons rise because heated air expands and becomes less dense.
175. State the difference between elastic and inelastic collisions.
     Answer: Elastic collisions conserve both momentum and kinetic energy; inelastic collisions conserve momentum but kinetic energy is lost.
     Example: Billiard balls collide elastically; car crashes are inelastic.
176. Explain the greenhouse effect.
     Answer: Earth’s atmosphere traps heat from the Sun, warming the planet.
     Example: Increased greenhouse gases lead to global warming.
177. Why is glass a poor conductor of heat?
     Answer: Glass particles are tightly bound and do not allow free movement of heat energy.
     Example: Window panes do not transfer heat quickly.
178. What is the role of the moderator in a nuclear reactor?
     Answer: It slows down neutrons to sustain controlled chain reactions.
     Example: Graphite or water acts as moderators.
179. How does a lightning conductor protect a building?
     Answer: It provides a safe path for lightning to reach the ground, preventing damage.
     Example: Lightning rods on tall buildings.
180. Explain why shadows are sharp when the light source is small.
     Answer: Small sources produce less diffraction and overlapping of light, creating sharp edges.
     Example: A candle flame casts a sharp shadow.
181. Why are sound waves reflected in a curved concave surface?
     Answer: The curved surface focuses sound waves at a point.
     Example: Parabolic microphones use this principle.