SET 04

SET 4: Competence-Based Conceptual Physics Questions and Answers

91. Explain why it is dangerous to handle electrical appliances with wet hands.
    Answer: Water is a good conductor of electricity. Wet hands lower body resistance, increasing the risk of electric shock.
    Example: If a person touches a live wire with wet hands, they can become a path for electric current, which can cause fatal shocks.
92. Why do metals expand when heated?
    Answer: Heating increases the kinetic energy of metal atoms, causing them to vibrate more and move apart.
    Example: Gaps are left in railway tracks to allow for expansion on hot days.
93. State the principle of flotation and give an example in real life.
    Answer: An object floats when it displaces a fluid equal to its own weight.
    Example: A ship floats because its shape displaces enough water to balance its weight.
94. Why are curved mirrors used in vehicles?
    Answer: Convex mirrors give a wider field of view, allowing drivers to see more of the road behind.
    Example: Side mirrors on cars.
95. Why is copper used for electrical wiring?
    Answer: It is a good conductor, ductile, and resistant to corrosion.
    Example: Almost all domestic wiring is made of copper.
96. Describe how a transformer works and its two types.
    Answer: A transformer uses electromagnetic induction to change the voltage of alternating current. Step-up increases voltage, step-down decreases voltage.
    Example: Phone chargers use step-down transformers.
97. State the difference between heat and temperature.
    Answer: Heat is energy transferred due to temperature difference; temperature is the measure of the average kinetic energy of particles.
    Example: A bucket of warm water has more heat than a cup of hot tea.
98. Why is mercury used in thermometers instead of water?
    Answer: Mercury expands uniformly, does not stick to glass, and has a wide temperature range.
    Example: Clinical thermometers use mercury.
99. What is the role of the vacuum in a thermos flask?
    Answer: The vacuum reduces heat loss by conduction and convection.
    Example: It helps keep tea hot or ice cold for hours.
100. State one difference between potential and kinetic energy with example.
     Answer: Potential energy is stored energy (e.g., a book on a shelf); kinetic energy is energy of motion (e.g., a falling book).
101. What is the function of a fuse in an electric circuit?
     Answer: To break the circuit when the current exceeds a safe level, preventing damage or fire.
     Example: A 13A fuse in a plug melts if current exceeds 13A.
102. Why does a ball bounce lower each time after hitting the floor?
     Answer: Energy is lost as sound, heat, and deformation on each impact, reducing rebound height.
103. What causes echoes and how can they be minimized in halls?
     Answer: Echoes are caused by sound reflections. They are minimized by using soft materials like curtains and carpets to absorb sound.
104. Why is it easier to lift a heavy object with a pulley system?
     Answer: Pulleys distribute weight and change direction of force, reducing effort needed.
     Example: Lifting cargo with a block-and-tackle system.
105. How is a rainbow formed?
     Answer: It forms due to refraction, dispersion, and reflection of sunlight in raindrops.
106. Give two uses of electromagnets in daily life.
     Answer: (1) In electric bells, (2) In scrap yard cranes to lift metal.
107. What is the purpose of using carbon brushes in electric motors?
     Answer: They maintain electrical contact with the rotating commutator, allowing current to flow.
108. What is the difference between static and current electricity?
     Answer: Static electricity is stationary charge; current electricity is the flow of electrons.
109. State the principle of moments and give an application.
     Answer: When a body is in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments.
     Example: Balancing a seesaw.
110. What causes the sensation of heat in metallic objects left in the sun?
     Answer: Metals are good conductors and absorb heat quickly from sunlight, raising their surface temperature.