Input/Output — Set 2

Correct Answer: A. Input

• **Light Pen (Input device)** = a stylus-shaped input device with a photosensor tip that detects the light pulse emitted by a CRT screen's electron beam as it sweeps across each pixel, allowing the user to point at or draw directly on the screen surface. • **CRT dependency** — light pens work by timing the screen's refresh scan; this mechanism is incompatible with modern LCD/LED panels that do not use a scanning electron beam, which is why they are obsolete today. • Early CAD software and graphical interfaces in the 1970s–80s relied on light pens before the mouse became widespread. • 💡 Option B (Output) is wrong because the light pen sends positional data into the computer rather than receiving data from it; Option C (Storage) is wrong because it holds no data; Option D (Processing) is wrong because processing is performed by the CPU, not an external pen device.

Correct Answer: C. Laser

• **Laser printer** = a non-impact printer that uses a focused laser beam to draw the page image onto a charged photosensitive drum — the drum then attracts dry toner powder only where the laser discharged the surface charge, and heat from a fuser roller bonds the toner permanently to paper. • **Static electricity role** — the drum is initially given a uniform negative charge; the laser neutralises selected spots, and the positively charged toner particles are attracted exactly to those neutralised areas, creating a precise image before paper even enters the heat zone. • Laser printers produce sharp, smear-proof text at speeds of 20–60 PPM and are the standard for high-volume office printing. • 💡 Option A (Inkjet) is wrong because inkjet printers spray liquid ink through microscopic nozzles, with no laser or toner powder involved; Option B (Thermal) is wrong because thermal printers use heat-sensitive paper and require no toner or laser; Option D (Daisy Wheel) is wrong because daisy wheel printers stamp pre-formed characters like a typewriter and cannot produce graphics.

Correct Answer: C. Barcode Reader

• **Barcode Reader** = an optical input device that illuminates the parallel black-and-white bars on a product label with a laser or LED and measures the reflected light — wide bars and narrow bars reflect differently, and the reader decodes that pattern into a numeric product ID used by the store database. • **Retail backbone** — the decoded number is matched against the store's POS system to retrieve the product name and price in milliseconds, drastically reducing checkout errors compared to manual entry. • 2D barcodes (QR codes) store far more data than traditional 1D barcodes and can be read by smartphone cameras as well as dedicated scanners. • 💡 Option A (OCR) is wrong because OCR reads printed text characters using image recognition, not bar-pattern product labels; Option B (MICR) is wrong because MICR reads magnetic ink characters on bank cheques, not product barcodes; Option D (OMR) is wrong because OMR detects pencil marks in pre-defined circles on answer sheets, entirely unrelated to product identification.

Correct Answer: A. Video Display Unit

• **Video Display Unit (VDU)** = a general-purpose term for any screen-based output device that presents computer-generated text and graphics — it encompasses CRT monitors, LCD flat panels, plasma displays, and projector screens, all of which deliver visual output from the computer. • **Resolution and refresh rate** — a VDU's sharpness is determined by pixel resolution (e.g., 1920x1080 Full HD), and its motion smoothness is determined by refresh rate in Hertz (Hz), typically 60–144 Hz for modern panels. • The term VDU was widely used in British and Commonwealth technical literature from the 1970s–90s and remains common in Indian competitive exam syllabi. • 💡 Option B (Virtual Data User) is wrong because this is a fabricated phrase with no standard meaning in computing; Option C (Visual Digital Utility) is wrong because this too is not a recognised computing term; Option D (Variable Drive Unit) is wrong because drive units refer to storage hardware, not display devices.

Correct Answer: D. Fingerprint Scanner

• **Fingerprint Scanner** = a biometric input device that captures a high-resolution image or capacitive map of the unique ridge-and-valley pattern on a fingertip and compares it against a stored template to verify the user's identity — this is the standard method for biometric authentication on smartphones and laptops. • **Why fingerprints are unique** — each person's fingerprint pattern forms randomly during fetal development and remains virtually unchanged throughout life, making it a reliable individual biometric identifier. • Modern fingerprint sensors are either optical (camera-based, often embedded under the display) or capacitive (detects electrical differences between skin ridges and valleys). • 💡 Option A (Touchpad) is wrong because a touchpad is a pointing device for cursor navigation, not biometric identification; Option B (Stylus) is wrong because a stylus is a pen-like tool for writing on touchscreens, with no identity-sensing capability; Option C (Trackball) is wrong because a trackball controls cursor movement using a rolling ball and has no biometric function.

Correct Answer: A. Pixels

• **Pixels** = the resolution of a monitor is measured in pixels (short for picture elements), where each pixel is the smallest individually controlled dot of colour on the screen — a resolution of 1920x1080 means 1,920 pixels across and 1,080 pixels down, giving about 2 million pixels total. • **Higher pixels = sharper image** — as pixel density increases (measured as PPI, pixels per inch), individual dots become invisible to the human eye and the image appears continuous and crisp, which is why 4K (3840x2160) screens look noticeably sharper than Full HD. • Common resolutions include HD (1280x720), Full HD (1920x1080), QHD (2560x1440), and 4K (3840x2160). • 💡 Option B (Inches) is wrong because inches measure the physical diagonal size of the monitor panel, not image detail; Option C (Centimeters) is wrong because centimeters also measure physical dimensions, not pixel count; Option D (Liters) is wrong because liters measure volume and have absolutely no relevance to screen display.

Correct Answer: C. Speakers

• **Speakers** = output devices that convert digital audio signals from the computer's sound card into mechanical vibrations via a magnetic voice coil and cone, producing audible sound waves that fill a room — unlike headphones, speakers broadcast sound outward so multiple people can hear simultaneously. • **Amplifier requirement** — most computer speakers have a built-in amplifier to boost the low-level audio signal from the sound card to a level powerful enough to drive the speaker cone; passive speakers require an external amplifier. • High-end 5.1 or 7.1 surround-sound speaker systems place multiple drivers around the room to create a three-dimensional audio experience for home theatres. • 💡 Option A (Microphone) is wrong because a microphone is an input device that captures sound, the exact opposite function; Option B (Headphones) is wrong because headphones deliver audio privately to a single user, not to multiple people in a room; Option D (Webcam) is wrong because a webcam is a visual input device that has nothing to do with audio output.

Correct Answer: C. Mouse

• **Mouse** = a trackball performs the same cursor-pointing function as a mouse — both move the on-screen pointer, have click buttons, and often a scroll wheel — but in a trackball the ball sits on top and is rolled by the user's thumb or fingers while the device body stays perfectly still. • **Ergonomic advantage** — because the trackball base never moves, it requires no desk space for sweeping motions and reduces wrist and arm strain, making it a preferred alternative for users with repetitive strain injuries. • Trackballs are common in industrial control panels, air-traffic control systems, and CAD workstations where space is limited. • 💡 Option A (Keyboard) is wrong because a keyboard is a text-input device with no cursor-pointing function comparable to a trackball; Option B (Scanner) is wrong because a scanner converts physical documents to digital images, a completely different function; Option D (Printer) is wrong because a printer is an output device that produces paper output.

Correct Answer: C. MICR

• **MICR (Magnetic Ink Character Recognition)** = a bank-cheque reading technology where the account number, cheque number, and branch code are printed at the bottom of a cheque in a special iron-oxide-based magnetic ink — a MICR reader magnetises these characters and reads the magnetic waveform pattern to decode the data. • **Fraud resistance** — because the ink itself must contain real magnetic particles to be read correctly, MICR characters are extremely difficult to forge with ordinary photocopiers or inkjet printers, making the system highly secure for high-volume financial processing. • MICR allows banks to process millions of cheques daily at speeds far beyond manual verification. • 💡 Option A (OMR) is wrong because OMR detects pencil-filled circles on answer sheets, not magnetic ink on cheques; Option B (OCR) is wrong because OCR uses optical image recognition of printed characters with regular ink, not magnetism; Option D (Barcode) is wrong because barcodes use light reflection off black-and-white stripes, not magnetic ink characters.

Correct Answer: D. To input live video and images

• **Input live video and images** = a webcam is a digital video input device that continuously captures frames from the real world and streams them to the computer in real time — it functions like a small camera permanently connected to the computer, feeding visual data inward. • **Video conferencing standard** — webcams became essential with the rise of platforms like Zoom, Teams, and Google Meet; most laptop webcams capture 720p or 1080p at 30 frames per second, while external webcams can reach 4K at 60 fps. • Webcams also support facial-recognition login (Windows Hello) and live-streaming on platforms like YouTube and Twitch. • 💡 Option A (To print photos) is wrong because printing is the function of a printer, not a camera-type input device; Option B (To display system errors) is wrong because system error messages are shown by the OS on the monitor, not by a webcam; Option C (To scan old negatives) is wrong because scanning film negatives requires a dedicated film scanner, not a webcam.