Physics Working Models for Science Exhibition

Why Physics Makes the Best Working Models

Physics is the branch of science most naturally suited to working models because almost every concept involves motion, force, energy transfer or electrical/magnetic effects — all of which can be demonstrated visibly. A chemistry experiment produces a reaction that may or may not be visible; a biology model often requires labelling to explain. But a physics working model that spins, lifts, lights up or balances demonstrates its concept by simply existing and operating.

The 15 models below span mechanics, electricity and magnetism, optics, and waves. Each one maps directly to a specific CBSE chapter, so choosing one that aligns with your current coursework gives you the double benefit of building something impressive and reinforcing a topic you need to know for your exam.

Models 1–5: Electricity and Magnetism

**1. DC Electric Motor** Concept: Magnetic force on a current-carrying conductor (Class 10, Chapter 13) Build: Wind 50 turns of enamelled copper wire on a rectangular cardboard frame. Sand the enamel off one full end of each wire and half the enamel off the other end (this acts as a commutator). Balance the coil horizontally on two safety pins connected to a battery. Place a strong magnet below. When the battery is connected, the coil spins. Materials: Enamelled copper wire, two safety pins, 9V battery, strong bar magnet, cardboard.

**2. Electromagnetic Crane** Concept: Electromagnet — current-controlled magnetic field (Class 10, Chapter 13) Build: Wind 150+ turns of insulated copper wire tightly around an iron bolt. Connect the ends to a battery via a switch. The bolt becomes a magnet when the switch is on and can pick up iron objects. Mount it on a cardboard arm to simulate a crane. Materials: Insulated copper wire, iron bolt, 9V battery, switch, paper clips, cardboard.

**3. Galvanometer Using a Compass** Concept: Magnetic effect of electric current (Class 10) Build: Coil 50 turns of wire on a rectangular frame. Place a compass inside the coil and connect the ends to a circuit. When current flows, the needle deflects. The more turns, the greater the deflection. This was how the first galvanometers worked. Materials: Compass, insulated wire, cardboard, battery, resistor.

**4. Transformer Model (Step-Up and Step-Down)** Concept: Mutual induction, AC transformers (Class 12 Physics, but demonstrable earlier) Build: Wind two coils of different turn counts on an iron core (a bundle of iron nails). Connect the primary coil to an AC source (use a small signal generator or a buzzer circuit). Connect the secondary to an LED or voltmeter. Show that more turns in the secondary = higher voltage. Materials: Insulated wire, iron nails, buzzer/AC adapter, LED, voltmeter.

**5. Ohm's Law Verification Circuit** Concept: Relationship between voltage, current and resistance (Class 10, Chapter 12) Build: Set up a circuit with a rheostat, ammeter, voltmeter and a resistor. Vary the resistance and record V and I at each setting. Plot a V-I graph — the straight line through the origin confirms Ohm's Law. The slope gives the resistance. Materials: Rheostat (or multiple resistors), ammeter, voltmeter, connecting wires, battery, bulb.

Models 6–10: Mechanics and Forces

**6. Hydraulic Lift** Concept: Pascal's law — pressure transmitted equally in all directions through a fluid (Class 11) Build: Connect two syringes of different sizes with plastic tubing filled with water. Push the small plunger in and the large plunger rises — multiplying force. Add a small platform to the large plunger and show it lifting a small load. Materials: Two syringes (10ml and 50ml), plastic tubing, water, food colouring (optional), cardboard platform.

**7. Newton's Cradle** Concept: Conservation of momentum and energy in elastic collisions (Class 9–10) Build: Suspend five equal steel ball bearings from a horizontal bar using pairs of strings so each ball hangs vertically and the balls just touch. Pull one end ball back and release. The ball at the opposite end swings out with the same velocity. Materials: 5 equal steel ball bearings, strong thread, two parallel horizontal bars, wooden frame.

**8. Inclined Plane Force Reduction** Concept: Mechanical advantage of an inclined plane (Class 9, work and energy) Build: Build a ramp at three different angles. Use a spring balance to measure the force needed to pull a fixed weight up the ramp vs lifting it vertically. Show that the gentler the angle, the less force needed but the more distance covered. Materials: Plank, hinge, protractor, spring balance, 500g weight.

**9. Simple Pendulum Time Period** Concept: Time period depends on length, not mass (Class 9, Gravitation) Build: Hang pendulums of 25cm, 50cm, 75cm and 100cm length from a horizontal rod. Time 20 complete oscillations for each. Calculate the time period (T = time for 20 / 20). Plot length vs T². Show the linear relationship. Materials: String, various weights (all the same mass), stopwatch, ruler.

**10. Bernoulli Effect Demonstrator** Concept: Faster-moving fluid has lower pressure (Bernoulli's principle — Class 11) Build: Hold two sheets of A4 paper parallel, 2–3 cm apart, and blow steadily between them. They move together instead of apart. Extend: suspend a ping-pong ball in a hairdryer airstream — it stays levitating in the centre. Demonstrate that aeroplanes generate lift the same way. Materials: A4 paper, ping-pong ball, hair dryer (optional).

Models 11–15: Optics, Sound and Energy

**11. Convex Lens Image Demonstrator** Concept: Image formation by a convex lens at different object distances (Class 10, Chapter 10) Build: Mount a convex lens (from a magnifying glass) vertically on a cardboard stand. Place a bright torch or candle on one side and a white screen on the other. Mark the principal focus using a parallel beam. Then show images formed at object distances: beyond 2F (real, inverted, diminished), at 2F (same size), between F and 2F (magnified). Materials: Magnifying glass, cardboard, white screen, torch.

**12. Periscope** Concept: Law of reflection — angle of incidence equals angle of reflection (Class 10) Build: Create a rectangular tube from cardboard. Cut two 45° windows at opposite ends on opposite sides. Mount mirrors at 45° angles at each window. When you look through one end, you can see objects above, below or around corners. Materials: Cardboard, two small mirrors, adhesive, protractor.

**13. Sound Wave Visualiser (Chladni Plate)** Concept: Sound as a standing wave produces regular node patterns (Class 9, Sound) Build: Stretch cling film tightly over the mouth of a metal or plastic container. Sprinkle salt or fine sand evenly. Hold a speaker (connected to a tone generator app on a phone) near the surface and vary the frequency. The salt moves to the nodes of the standing wave and forms symmetric patterns. Materials: Container, cling film, fine salt or sand, phone with tone generator app.

**14. Solar Cell Efficiency Comparator** Concept: Photovoltaic effect — light energy converts to electrical energy (Class 12 / general) Build: Connect a small solar panel to a voltmeter. Place it at different distances from a lamp and at different angles to the light source. Record voltage at each position. Show that maximum output is at 90° (perpendicular to the light source) and decreases as the angle changes. Materials: Small solar panel (₹80–120 from electronics shops), voltmeter, lamp, protractor.

**15. Windmill Generator** Concept: Kinetic energy of wind converts to electrical energy (electromagnetic induction) Build: Attach fan blades (cardboard or plastic spoons) to the axle of a small DC motor salvaged from a toy. Connect the motor terminals to an LED. Mount the assembly on a stand. Blow on the blades with a hair dryer or in a breeze — the LED lights up. Vary the wind speed and show that higher speed = brighter LED. Materials: Small DC motor (from a toy), fan blades or plastic spoons, LED, wire, wooden stand.

How to Explain Your Physics Model to Judges

For any physics working model, your explanation should follow this four-part structure: (1) Name the principle or law — 'This demonstrates Pascal's Law of fluid pressure.' (2) Explain the input — 'When I push this small syringe...' (3) Explain the output — '...this large platform rises.' (4) Explain why — 'This is because pressure applied to an enclosed fluid is transmitted equally in all directions, so the larger piston area means a larger force for the same pressure.'

Practice until you can deliver this in under 90 seconds without notes. Judges at senior level will then ask a follow-up. The most common follow-up for physics models is: 'What is the real-world application of this?' Have one good answer ready. For the hydraulic lift: JCB excavators, car hydraulic jacks, aircraft landing gear. For the DC motor: every electric fan, washing machine and power tool. This shows you understand why the concept matters.