physics

Time switch

Time switch is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Time switch rather than just read about it. In short: A time switch (also called a timer switch, or simply timer) is a device that operates an electric switch controlled by a timer. Intermatic introduced its first time switch in 1945, which was used for "electric signs, store window lighting, apartment hall lights, stokers, and oil and gas burners." A consumer version was added in 1952.

Key takeaways

Time switch belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Time switch to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Time switch from memory before moving on to harder problems.

Reference excerpt

A time switch (also called a timer switch, or simply timer) is a device that operates an electric switch controlled by a timer. Intermatic introduced its first time switch in 1945, which was used for "electric signs, store window lighting, apartment hall lights, stokers, and oil and gas burners." A consumer version was added in 1952. The switch may be connected to an electric circuit operating from mains power, including via a relay or contactor; or low voltage, including battery-operated equipment in vehicles. It may be built into power circuits (as with a central heating or water heater timer), plugged into a wall outlet with equipment plugged into the timer instead of directly into the power point; or built into equipment. The mechanism may be mechanical (e.g., clockwork; rarely used nowadays), electromechanical (e.g., a slowly rotating geared motor that mechanically operates switches) or electronic, with semiconductor timing circuitry and switching devices and no moving parts.

Applications A timer may switch equipment on, off, or both, at a preset time or times, after a preset interval, or cyclically. A countdown time switch switches power, usually off, after a preset time. A cyclical timer switches equipment both on and off at preset times over a period, then repeats the cycle; the period is usually 24 hours or 7 days. For example, a central heating timer may supply heat for a specified period during the morning and evening every weekday, and all day on weekends. A timer for an unattended slow cooker may switch on automatically at a time and for a period suitable to have food ready at mealtime. Likewise, a coffee maker may turn itself on early in the morning in time for awakening residents to have fresh coffee already brewed for them. Timers may do other processing or have sensors; for example, a timer may switch on lights only during hours of darkness, using a seasonal algorithm or light sensor. Combining the two allows a light to come on at sundown and go off at midnight, for example. Time switches can be used for many purposes, including saving electric energy by consuming it only when required, switching equipment on, off, or both at times required by some process, and home security (for example switching lights in a pattern that gives the impression that premises are attended) to reduce the likelihood of burglary or prowling. Among applications are lighting (interior, exterior, and street lighting), cooking devices such as ovens, washing machines, and heating and cooling of buildings and vehicles. Built-in automatic washing machine controllers are examples of very complex electromechanical and electronic timers cycles, starting and stopping many processes including pumps and valves to fill and empty the drum with water, heating, and rotating at different speeds, with different combinations of settings for different fabrics.

Types

Sleep timer A sleep timer is a function on many modern televisions and other electronic devices that shuts off the power after a preset amount of time. The setting is usually made either from the remote control of the device or the device's menu. They are intended to allow viewers to watch as they fall asleep.

Astronomical timer An astronomical (or astronomic) timer calculates dawn and dusk times (tracking the sun position) for each day of the year based on the latitude and longitude (or just north/central/south and time zone on more cheaply made ones), and the day of the year (month and date), programmed by the user upon installation in addition to the usual time of day, except in the case of GPS enabled astronomic timers wherein all programming is fully automatic. This eliminates the need for a photocell (which may be repeatedly triggered on and off by the light which it operates) or for repeatedly re-setting a regular timer for seasonal changes in the length of day or for daylight-saving time. This allows exterior lighting like a porch light fixture to be controlled by simply replacing its indoor wall switch, or doing the same for a lamp in a dark interior corner (away from a window) by simply plugging-in a self-adjusting lamp timer.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with Time switch

Start with the simplest possible case. Write down what Time switch claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Time switch before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Time switch ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Time switch

In research: Time switch appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Time switch in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Time switch is common in secondary-school and first-year university syllabi. It links to neighbouring topics Appropriate technology, Energy development, Switches, so understanding it makes those chapters shorter.
In everyday life: Look for Time switch outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Time switch in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Time switch means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Time switch out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Time switch in simple terms?

Why does Time switch matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Time switch?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Time switch.