Sensors: how machines feel the world
A sensor is a small device that changes something in the world (touch, light, heat, movement) into an electric signal that a chip can read.
- Touch screen: the glass holds a thin electric field. Your finger is slightly conducting, so it changes the field at one spot. The phone finds that spot.
- Light sensor and camera: light hits a tiny chip and knocks out electrons. More light means a bigger signal. Millions of such spots make a picture.
- Motion sensor (accelerometer): a tiny moving part shifts when you tilt or shake the phone, and the shift becomes a signal. This turns the screen sideways.
- Temperature, sound, pressure sensors: each changes one signal when its condition changes.
Rule: sensor → signal → chip decides → output.
Chips and batteries: the brain and the energy
A chip is a small slab of silicon. Silicon is a semiconductor: it conducts a little, and we can switch it between conducting and not conducting. Billions of tiny switches (transistors) are printed on one chip. They work in 1s and 0s and do calculations.
A lithium-ion battery stores energy by moving lithium ions between two layers (electrodes). Charging pushes the ions into one side. Using the phone lets them flow back and gives electric current.
Energy of a battery (in watt-hours) = voltage (V) × capacity (Ah). A 3.7 V, 5 Ah battery stores 3.7 × 5 = 18.5 Wh.
New materials: arrangement is power
Different materials can be made of the same atom. Carbon shows this best:
- Graphite: flat layers that slide over each other. Soft, and a pencil lead leaves a mark.
- Diamond: every carbon atom has 4 strong bonds in 3D. Hardest natural material.
- Graphene: one single layer of graphite. It is only one atom thick, very strong for its weight, bendy, and conducts electricity and heat very well.
Other advanced materials: shape-memory alloys that return to their shape when warmed, polymers (plastics) that are light and tough, composites (carbon fibre in plastic) used in aircraft and bikes, and nanomaterials (parts only a few billionths of a metre across).
Idea: change how atoms are arranged, and you change what the material can do.
How new medicines are made
Most diseases involve a molecule in our body or in a germ (a target). A medicine is a molecule shaped to fit the target, like a key in a lock. When it fits, it can block a germ's enzyme or calm an overactive cell.
- Find a target that causes the disease.
- Search or design molecules that fit it. Computers and AI can test millions of shapes quickly.
- Lab tests on cells and then on animals (as little as possible) for safety.
- Clinical trials in people: small groups first for safety, then bigger groups to see if it works, compared with a dummy pill (placebo).
- Approval and watching side effects after it is sold.
Vaccines work in a similar way: they teach the body to recognise a germ's marker before the germ arrives. This whole process often takes 10 years or more, because safety matters most.
Trends: where science and technology are heading
Fields used to be separate: biology, computing, materials. Today they converge (join):
- Biology + information: bioinformatics, reading and editing DNA with computers, AI drug design.
- Biology + nano: nano-medicine, tiny carriers that bring a drug straight to a sick cell.
- Information + nano: smart sensors and very small, fast chips.
- All three: wearable patches that sense the body, analyse the signal and report to a doctor.
Other trends: clean energy and better batteries, robots that work with people, and space and ocean technology. Each new power brings choices: privacy, fairness, safety and cost. A good scientist asks "can we?" and also "should we, and for whom?".
Try it: spot the science
Try it at home: list 5 sensors you meet today (phone, lift, door light, thermometer, fitness band). For each one write what it senses and what it does.
Try it in 3D: in the medicine view, set the three sliders so the drug fits the target. Then change one slider by one step. What happens? Why is a nearly right shape not enough?
Key formulas and definitions
- Sensor chain: sensor → electric signal → chip → output
- Battery energy (Wh) = V × Ah
- Current I = P ÷ V (charger power ÷ voltage)
- Carbon forms: graphite (layers), diamond (3D network), graphene (one layer)
- Drug works when its shape fits the target (key and lock)
- Medicine path: target → design → lab test → trials → approval
Worked examples
1. Name the sensor that turns your phone screen sideways when you rotate it.
The motion sensor (accelerometer). It feels the pull of gravity on a tiny part and sends a signal that changes with tilt.
2. A battery is 3.7 V and 5 Ah. How much energy does it store?
Energy = V × Ah = 3.7 × 5 = 18.5 Wh.
3. A phone charger gives 12 W at 5 V. What current does it supply?
I = P ÷ V = 12 ÷ 5 = 2.4 A.
4. Graphite and diamond are both carbon. Why is one soft and the other very hard?
In graphite the atoms sit in flat layers that slide over each other. In diamond every atom is locked in strong bonds in all 3 directions.
5. A phone battery is 3.7 V and 4 Ah. The phone uses 2 W. About how long will it last?
Energy = 3.7 × 4 = 14.8 Wh. Time = 14.8 ÷ 2 = 7.4 hours.
6. Why do medicines go through trials in people before approval?
To check safety first and then check that they really work, compared with a placebo. A medicine that fits its target in the lab can still be unsafe or useless in the body.
Common mistakes
- Thinking technology is magic. Every device is a chain of simple science ideas: sense, signal, decide, act.
- Saying graphite and diamond are different atoms. Both are carbon, only the arrangement differs.
- Believing a drug that works in a dish is ready to sell. It must pass safety tests and trials in people first.
- Mixing battery units: mAh is capacity, not energy. Energy needs voltage too (Wh = V × Ah).