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ICSE Class 7 Science★ ICSE Class 7 Physics · Full Year Coverage · Board: ICSE

Physics — Measurement, Motion, Heat, Light & Sound

PHYSICS for Class 7: How do we measure SPEED? What IS heat, and how does it travel? Why do we see our reflection in a mirror? And what IS sound — how does it reach our ears? ICSE Class 7 Science.

⏱ 16 min readMedium difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Calculate speed using Speed = Distance/Time; distinguish uniform from non-uniform motion
2Classify motion as rectilinear, circular, or periodic/oscillatory with examples
3State 3 modes of heat transfer; explain which one works without a medium (radiation)
4State the 5 properties of a plane mirror image
5Distinguish concave (torch/shaving mirror) from convex (rear-view mirror) mirrors by use
6State 3 characteristics of sound: pitch (frequency), loudness (amplitude), quality/timbre
7Distinguish series from parallel circuits; explain why household wiring uses parallel
8Explain how an electromagnet works and state its key feature (can be switched on/off)

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Why this chapter matters

This ICSE Class 7 Physics chapter covers all major physics topics tested in the annual exam: speed calculation (distance/time), types of motion, three modes of heat transfer (conduction/convection/radiation — especially radiation needs no medium), plane mirror image properties (virtual, erect, same size, laterally inverted), concave vs convex mirror uses, characteristics of sound (pitch, loudness, quality), series vs parallel circuits (household wiring = parallel), and electromagnets. The plane mirror 5-property question is tested every year. The heat transfer comparison table (mode/medium required/example) is a reliable 3-4 mark question.

Before you start — revise these

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Physics — Motion, Heat, Light, Sound & Electricity

1. Physical Quantities and Measurement

Speed

Speed = Distance / Time. Unit: m/s or km/h.
Average Speed = Total Distance / Total Time.

Area

Rectangle: Area = l × w. Square: s².
Circle: πr².
Irregular shapes: Use GRAPH PAPER. Count full squares. Estimate partial squares.

2. Motion

Types of Motion

Type	Example
Rectilinear	Straight line. Car on straight road.
Circular	Round and round. Fan, Earth around Sun.
Periodic/Oscillatory	Back and forth. Pendulum. Swing.

Uniform vs. Non-uniform Motion

Uniform: Equal distance in EQUAL time intervals. Constant SPEED.
Non-uniform: Speed CHANGES.

Distance-Time Graph

STRAIGHT line → uniform speed. CURVED line → acceleration/deceleration.

3. Heat

What Is Heat?

A form of ENERGY that flows from a HOTTER body to a COLDER body.

Temperature

Measured by a THERMOMETER. Units: Celsius (°C), Fahrenheit (°F), Kelvin (K).

Modes of Heat Transfer

Mode	How It Travels	Needs Medium?	Example
Conduction	Particle to particle (solids)	YES	Metal rod heated at one end
Convection	Movement of the fluid itself (liquids/gases)	YES	Water boiling. Sea breeze.
Radiation	Electromagnetic waves. NO particles needed.	NO. Can travel through VACUUM.	Sun's heat reaching Earth.

Good and Poor Conductors

Conductors: Metals (copper, aluminium). TRANSFER heat quickly.
Insulators: Wood, plastic, air, glass wool. TRANSFER heat SLOWLY.

4. Light

Rectilinear Propagation

Light travels in STRAIGHT LINES. Evidence: Shadows. Pinhole camera.

Reflection

Light BOUNCES off a surface. Angle of incidence = Angle of reflection.

Plane Mirror

Image is: (a) VIRTUAL (cannot be caught on a screen), (b) ERECT (upright), (c) SAME SIZE as object, (d) LATERALLY INVERTED (left ↔ right swapped), (e) As far BEHIND the mirror as the object is in FRONT.

Spherical Mirrors

Type	Shape	Image
Concave	Curved INWARD (like a bowl)	Can be REAL and MAGNIFIED. Used in torches, shaving mirrors.
Convex	Curved OUTWARD (bulging)	Always VIRTUAL, DIMINISHED (smaller). Wider field of view. Used in rear-view mirrors.

5. Sound

What Is Sound?

Sound is produced by VIBRATIONS. It travels as WAVES through a medium (solid, liquid, gas). Sound CANNOT travel through VACUUM.

Characteristics of Sound

Characteristic	What It Is
Pitch	How HIGH or LOW a sound is. Depends on FREQUENCY (vibrations per second). High frequency = high pitch.
Loudness	How LOUD or SOFT. Depends on AMPLITUDE.
Quality (Timbre)	What makes a flute sound DIFFERENT from a violin playing the same note

6. Electricity and Magnetism

Electric Current

Flow of ELECTRONS through a conductor. Measured in AMPERES (A). Needs a COMPLETE PATH (circuit) to flow.

Circuit Symbols

Battery (—|⊢—), Bulb (—⨂—), Switch (— / — open, — — closed).

Types of Circuits

Series: Single path. If one bulb fuses → ALL go off.
Parallel: Multiple paths. If one bulb fuses → others stay ON. 'Household wiring is PARALLEL.'

Magnets

Every magnet has a NORTH and SOUTH pole.
Like poles REPEL. Unlike poles ATTRACT.
Earth = GIANT MAGNET. A freely suspended magnet ALIGNS NORTH-SOUTH (compass principle).

Electromagnet

When electric current flows through a coil of wire wrapped around an IRON core → it becomes a MAGNET. Switching OFF the current → magnetism DISAPPEARS.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Motion, Heat, Light, Sound, and Electricity

SPEED = Distance ÷ Time. Units: m/s or km/h. AVERAGE SPEED = Total Distance ÷ Total Time. AREA: Rectangle = l×w. Circle = πr². Graph paper for irregular shapes. TYPES OF MOTION: RECTILINEAR (straight line: car on road). CIRCULAR (round and round: fan, Earth around Sun). PERIODIC/OSCILLATORY (back and forth: pendulum, swing, vibrating string). UNIFORM motion: equal distance in equal time (constant speed). NON-UNIFORM: speed changes. DISTANCE-TIME GRAPH: straight line = uniform speed. Curved = acceleration/deceleration. HEAT: Heat flows from HOTTER → COLDER body. Temperature measured in °C/°F/K. THREE MODES OF HEAT TRANSFER: CONDUCTION (particles collide and pass heat — solids, needs MEDIUM). CONVECTION (fluid itself moves carrying heat — liquids/gases, needs MEDIUM). RADIATION (electromagnetic waves, NO MEDIUM needed — can travel through VACUUM). Example: Sun's heat reaches Earth by radiation. CONDUCTORS: metals (copper, aluminium). INSULATORS: wood, plastic, air, glass wool. LIGHT: travels in STRAIGHT LINES. REFLECTION: angle of incidence = angle of reflection. PLANE MIRROR IMAGE: (1) VIRTUAL (cannot catch on screen). (2) ERECT (upright). (3) SAME SIZE as object. (4) LATERALLY INVERTED (left↔right swapped). (5) As far BEHIND mirror as object is in FRONT. CONCAVE MIRROR (curved INWARD): real and magnified image possible. Uses: torches, shaving mirrors, satellite dishes. CONVEX MIRROR (curved OUTWARD): image always virtual, diminished (smaller), wider field of view. Uses: REAR-VIEW MIRRORS, security mirrors. SOUND: produced by VIBRATIONS. Travels as WAVES through MEDIUM (solid/liquid/gas). CANNOT travel through VACUUM. CHARACTERISTICS: PITCH = how high/low (depends on FREQUENCY — vibrations per second). High freq = high pitch. LOUDNESS = how loud/soft (depends on AMPLITUDE). QUALITY/TIMBRE = what makes flute and violin sound different at same pitch. ELECTRICITY: ELECTRIC CURRENT = flow of electrons. Measured in AMPERES (A). Needs COMPLETE PATH (circuit). SERIES CIRCUIT: single path. One bulb fuses → ALL go off. PARALLEL CIRCUIT: multiple paths. One fuses → others stay ON. HOUSEHOLD WIRING = PARALLEL (so each appliance works independently). ELECTROMAGNET: current through coil of wire around iron core → becomes a magnet. Switch OFF current → magnetism DISAPPEARS. Unlike a permanent magnet, it can be turned on and off.

ICSE CLASS 7 PHYSICS KEY FACTS: (1) RADIATION needs NO MEDIUM — it can travel through vacuum. This is how the Sun's heat/light reaches Earth (space is a vacuum). Conduction and convection both NEED a medium (material to travel through). (2) CONCAVE mirror = caved in (like a cave). Converging. CONVEX = bulging outward. Diverging. Remember: CONCAVE is used where you want MAGNIFICATION (shaving mirror), CONVEX is used where you want WIDE VIEW (rear-view mirror). (3) PLANE MIRROR image is LATERALLY INVERTED — left and right are swapped, NOT up and down. If you raise your RIGHT hand, your image raises its LEFT hand. (4) HOUSEHOLD WIRING: Parallel means each switch works INDEPENDENTLY. That's why turning off one light doesn't turn off all lights. (5) PITCH depends on FREQUENCY (not volume). LOUDNESS depends on AMPLITUDE (not frequency). These are often confused.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Saying radiation needs a medium to travel (like conduction and convection)

✓ RADIATION is the ONLY mode of heat transfer that does NOT need a medium. Conduction = heat passes through particles touching each other (needs a solid medium). Convection = hot fluid rises and cold fluid sinks (needs a liquid or gas medium). RADIATION = heat travels as electromagnetic waves (infrared radiation) through EMPTY SPACE. Proof: The Sun is ~150 million km away in EMPTY SPACE (vacuum). Yet its heat reaches us. This can ONLY happen by radiation — not conduction (no material connecting Sun to Earth) and not convection (no fluid in space). Exam: 'Heat from the Sun reaches Earth by ___.' Answer: RADIATION.

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1MEDIUM· heat-transfer-plane-mirror

Describe the three modes of heat transfer. Which mode operates in a vacuum? Then state all 5 properties of an image formed in a plane mirror.

▶ Show solution

THREE MODES OF HEAT TRANSFER: (1) CONDUCTION: Heat transfers through a material by particles VIBRATING and colliding with adjacent particles — passing energy along. REQUIRES A MEDIUM (usually solid). Example: Heat from a stove burner passes through a metal pan to the food. Metals are good conductors; wood and plastic are insulators. (2) CONVECTION: Heat transfers through MOVEMENT of the fluid itself. Hot fluid becomes less dense and RISES; cool fluid sinks to replace it — forming CONVECTION CURRENTS. REQUIRES A MEDIUM (liquid or gas). Example: Water boiling in a pot. Sea breeze (sea heats air in day → air rises → land breeze replaces). (3) RADIATION: Heat travels as ELECTROMAGNETIC WAVES (infrared radiation). DOES NOT REQUIRE A MEDIUM — can travel through VACUUM. Example: The Sun's heat reaches Earth through 150 million km of empty space. Dark/rough surfaces absorb and emit radiation better than shiny/smooth surfaces. HEAT TRANSFER IN VACUUM = RADIATION ONLY. PLANE MIRROR IMAGE — 5 PROPERTIES: (1) VIRTUAL — the image cannot be caught on a screen; it appears to be behind the mirror. (2) ERECT (UPRIGHT) — the image is the right way up. (3) SAME SIZE — the image is the same size as the object (neither magnified nor diminished). (4) LATERALLY INVERTED — left and right are SWAPPED (your left hand appears as the right hand in the mirror). (5) SAME DISTANCE — the image is as far behind the mirror as the object is in front of it.

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