Computer Science: Unit-wise Subjective Question Bank

Short 1. Bandwidth is the maximum amount of data a link can carry per second; throughput is the amount actually delivered per second. Both are measured in bps, Mbps or Gbps.

Short 2. Simplex: data flows in one direction only, e.g. TV broadcasting. Half duplex: data flows both ways but one way at a time, e.g. a walkie-talkie.

Short 3. Copper Ethernet is limited to 100 m per run, while fibre carries data for kilometres; and fibre carries light, so lightning and electrical noise between the buildings cannot disturb it (it is also faster).

Short 4. A switch joins devices within one LAN and forwards frames by MAC address; a router joins different networks (a LAN and the Internet) and forwards packets by IP address, choosing the best path.

Short 5. 1.2 GB = 1,200 MB = 1,200 × 8 = 9,600 Mb; time = 9,600 ÷ 50 = 192 s = 3.2 minutes.

Short 6. IPv4 addresses are 32 bits, written as four decimal numbers with dots (192.168.1.1); IPv6 addresses are 128 bits, written as eight hexadecimal groups with colons (2001:db8::1). IPv4 offers about 4.3 billion addresses, IPv6 about 3.4 × 10³⁸.

Short 7. ping checks whether another computer or website can be reached and shows the time each reply takes; ipconfig shows this computer's IP address, subnet mask and default gateway.

Short 8. An intranet is a private network for an organisation's own staff, e.g. a bank's staff portal; an extranet opens part of it to selected outsiders, e.g. a supplier portal where shops check their orders.

Long 1. Bus: all nodes on one backbone cable with terminators — uses the least cable. Ring: each node joined to the next in a closed loop, data in one direction — no collisions. Star: every node cabled to a central switch — one faulty cable affects only one computer and faults are easy to find. Mesh: nodes joined by many links — data takes another path if a link fails. (A tree or hybrid is also acceptable.) Each needs a small labelled sketch.

Long 2. Guided media carry signals along a cable — twisted pair, coaxial, optical fibre. Unguided media carry electromagnetic waves through air or space — radio, microwave, infrared, satellite, Wi-Fi, Bluetooth. Differences: guided media give a fixed path and are little affected by weather, while unguided signals spread out and are weakened by walls and rain; guided media are harder to tap, while unguided media allow devices to move freely.

Long 3. An IP address is the logical number given to every device on a network to identify it and route data to it. Private addresses (10.x, 172.16–31.x, 192.168.x) are used inside LANs and not routed on the Internet; public addresses are unique worldwide and assigned by ISPs, e.g. 8.8.8.8. Static addresses are set by hand and never change, e.g. a printer at 192.168.1.20; dynamic addresses are given by DHCP for a lease period, e.g. a phone joining Wi-Fi.

Long 4. Client–server: dedicated servers provide services to clients; central control, strong security and central backup; costly; suits large networks. Peer-to-peer: all computers equal, each shares its own resources; cheap and simple, but weak security and separate backups; suits about ten computers. A bank must use client–server, because customer accounts need central security, access control, backup and many simultaneous users.

Short 1. A primary key uniquely identifies each record and cannot be NULL, e.g. roll in students. A foreign key is a field that refers to the primary key of another table, e.g. roll in marks referring to students(roll).

Short 2. DDL defines the structure of the database — CREATE, ALTER, DROP; DML works on the data in the tables — INSERT, SELECT, UPDATE, DELETE. DDL changes are committed at once; DML changes can be undone inside a transaction.

Short 3. Searching, sorting and updating take seconds instead of hours; and keys and constraints stop duplicate or invalid entries (also security, backup, many users at once).

Short 4. A composite key is a key made of two or more fields that together identify a record; it is needed when no single field is unique, e.g. (roll, subject) in a marks table, where a student has many subjects.

Short 5.

SELECT name FROM students WHERE name LIKE 'S%';

On the students table of the DBMS chapter it returned Subigya Nepal and Sampada Bhattarai.

Short 6. DELETE (DML) removes chosen rows or all rows but keeps the table; DROP (DDL) removes the whole table, its structure and data, permanently.

Short 7. (a) One-to-one — each citizen has one certificate and each certificate belongs to one citizen. (b) One-to-many — one class teacher has many students, but each student has one class teacher.

Long 1. A DBMS is software that creates, stores, retrieves, updates and manages data in a database, e.g. MySQL. Features: data storage in tables of rows and columns; data retrieval with queries in seconds; data integrity through keys and constraints such as CHECK; security through accounts and permissions; backup and recovery; control of redundancy (any three, one mark each).

Long 2.

SELECT name, salary FROM staff WHERE salary BETWEEN 30000 AND 50000;
SELECT name FROM staff ORDER BY name;
UPDATE staff SET post = 'Head' WHERE sid = 5;
DELETE FROM staff WHERE post = 'Peon';

On six sample records, (a) returned Gita Sharma 42000.00, Hari Thapa 38000.00 and Mohan Rai 46000.00; (b) listed Bina KC, Gita Sharma, Hari Thapa, Mohan Rai, Ram Lama, Sita Magar; (c) changed 1 row; (d) removed 2 rows, leaving four staff.

Long 3. One-to-one: one record matches exactly one, e.g. person — passport; stored by putting one table's primary key as a unique foreign key in the other. One-to-many: one record matches many, each of which matches one, e.g. teacher — classes; the foreign key goes in the "many" table. Many-to-many: many match many, e.g. students — courses; stored with a junction table enrolment(roll, course_code) holding both keys.

Short 1. Multimedia is the combined use of text, graphics, audio, video and animation to present information. In business it is used for advertisements and product videos, and for presentations and video meetings.

Short 2. Raster graphics are grids of pixels and pixelate when enlarged; vector graphics are mathematical shapes and stay sharp at any size. Raster suits photographs (JPG, PNG), vector suits logos (SVG).

Short 3. Lossless compression makes a file smaller without losing any detail (PNG, FLAC); lossy compression throws away detail that is hard to notice, giving much smaller files (JPG, MP3).

Short 4. Frame rate is the number of frames shown each second (fps), e.g. 30 fps; resolution is the number of pixels in each frame, width × height, e.g. 1920 × 1080.

Short 5. PNG is lossless and supports a transparent background, so a logo keeps sharp edges and sits cleanly on any colour. JPG's lossy compression makes photographs much smaller with no visible loss, while PNG photos would be very large.

Short 6. Typography is the art of arranging text for readability and appearance. Rules: use at most two fonts; make headings much larger than body text, with strong contrast between text and background.

Short 7. 2D animation has width and height only and looks flat; 3D has depth, perspective, light and shadow. 2D is drawn or built from flat parts; 3D is modelled, rigged and rendered.

Long 1. (1) Open pixlr.com → Pixlr Express → Create new; type a name and a size such as 1920 × 1080 → Create. (2) Choose the Text tool → Add new text, type the title and set font, size and colour; add a shape from Arrange/Elements → Shape and set its fill. (3) In the Layers panel add, rename, hide, lock or reorder layers so that the background, photo and text stay separate. (4) Click Save, choose PNG (or JPG), set the quality and Save as.

Long 2. (a) 3 × 60 × 30 = 5,400 frames. (b) 1920 × 1080 × 3 = 6,220,800 bytes (about 6.2 MB). (c) 10,000,000 × 180 = 1,800,000,000 bits; ÷ 8 = 225,000,000 bytes = 225 MB. (d) Uncompressed, the video would need 6.2 MB × 5,400 ≈ 33.6 GB; codecs such as H.264 make it small enough to store, upload and stream.

Long 3. Frame-by-frame animation draws every frame separately, e.g. a hand-drawn cartoon at 24 drawings per second. Keyframe animation sets only the key positions and the software calculates the in-between frames, e.g. a ball placed at the start and end of its path. Uses in education: animated science processes such as the water cycle or a beating heart; simulations and interactive lessons such as E-Paath.

Short 1.

def simple_interest(p, t, r):
    return p * t * r / 100

print("Simple interest:", simple_interest(5000, 2, 10))

Output: Simple interest: 1000.0.

Short 2.

try:
    age = int(input("Enter your age: "))
    print("In five years you will be", age + 5)
except ValueError:
    print("Please type your age in digits, for example 15.")

Typing "fifteen" prints the message; typing 15 prints In five years you will be 20.

Short 3. The loop multiplies total by 1, 2, 3 and 4: 1 × 1 × 2 × 3 × 4 = 24 (it computes 4!).

Short 4. A local variable is created inside a function and exists only there; a global variable is created outside all functions and can be read anywhere. In x = 10 followed by def f(): y = 5, x is global and y is local — print(y) outside f gives a NameError.

Short 5. "w" erases the file's old content and writes from the start; "a" keeps the old content and adds the new data at the end. Both create the file if it does not exist.

Short 6.

import turtle
t = turtle.Turtle()
for i in range(4):
    t.forward(120)
    t.right(90)
turtle.done()

Short 7.

import pandas as pd
df = pd.read_csv("marks.csv")
print("Average marks:", df["Marks"].mean())

With marks 78, 64, 91 and 55 it printed Average marks: 72.0.

Short 8. The provinces are separate categories to be compared, and bars of different lengths show at a glance which province has the most and the fewest people; a line chart would wrongly suggest a trend between provinces.

Long 1.

def grade(p):
    if p >= 90:
        return "A+"
    elif p >= 80:
        return "A"
    elif p >= 70:
        return "B+"
    elif p >= 60:
        return "B"
    elif p >= 50:
        return "C+"
    elif p >= 40:
        return "C"
    elif p >= 35:
        return "D"
    else:
        return "NG"

for p in [55, 82.5, 91, 33]:
    print(p, "->", grade(p))

55 -> C+
82.5 -> A
91 -> A+
33 -> NG

Long 2.

import pandas as pd

data = {"Name": ["Asmita", "Bijay", "Chandani", "Dipesh"],
        "Club": ["Science", "Sports", "Coding", "Eco"],
        "Score": [78, 64, 91, 70]}
pd.DataFrame(data).to_csv("club.csv", index=False)

df = pd.read_csv("club.csv")
print(df[df["Score"] > 70])

       Name     Club  Score
0    Asmita  Science     78
2  Chandani   Coding     91

Dipesh's 70 is not more than 70, so he is left out.

Long 3.

import matplotlib.pyplot as plt

items = ["Food", "Rent", "Education", "Others"]
amount = [15000, 10000, 8000, 7000]

plt.pie(amount, labels=items, autopct="%1.1f%%")
plt.title("Monthly expenses of a family")
plt.show()

Food is 15,000 ÷ 40,000 × 100 = 37.5 %, the largest slice.

Long 4.

name = input("Enter file name: ")
try:
    f = open(name, "r")
    print(f.read())
    f.close()
except FileNotFoundError:
    print("File", name, "was not found.")
finally:
    print("Done")

For a missing file it printed File notes.txt was not found. and then Done; for an existing file it printed the file's contents and then Done.

Short 1. AI is the branch of computer science that makes machines do tasks needing human intelligence, such as reasoning and understanding language. ML is the part of AI in which machines learn from data and improve with experience.

Short 2. Supervised learning trains on labelled data, e.g. emails marked spam or not spam; unsupervised learning finds groups in unlabelled data, e.g. grouping customers by shopping habits.

Short 3. Reinforcement learning is learning by trial and error: an agent acts, receives rewards or penalties, and learns the actions that earn most reward — e.g. a robot learning to walk or a program learning to play a game.

Short 4. It can produce false information confidently (hallucination); and it can repeat bias from its training data (also out-of-date knowledge, privacy risks, copyright issues).

Short 5. Sense: sensors collect information; think: the controller or AI decides what to do; act: actuators such as motors carry out the action.

Short 6. IoT is the network of everyday objects with sensors and Internet connections that collect and share data and act on it. Home examples: smart bulbs or plugs controlled from a phone; a doorbell camera that sends alerts.

Short 7. VR replaces the real world with a computer-made 3D world seen through a headset, e.g. a VR game; AR adds digital information on top of the real world through a phone or glasses, e.g. Google Lens translating a sign.

Short 8. IaaS provides virtual servers, storage and networks managed by the customer's IT staff, e.g. Amazon EC2; SaaS provides complete applications used through a browser, e.g. Gmail or Google Docs.

Short 9. Faster service without queues, e.g. applying for a passport online; and transparency, e.g. tracking applications and seeing SEE results online (also less corruption, and services such as the Nagarik App from any district).

Long 1. An LLM is trained on huge amounts of text to predict the next token (word piece); when given a prompt it writes the answer one token at a time, choosing likely tokens, so it does not look facts up. An image generator (diffusion model) learns from pictures and captions; it starts from random noise and removes the noise step by step, guided by the prompt, until an image forms. Prompt tips: state the task, audience, length and format clearly; give context or an example, and refine the prompt if the first answer is not right.

Long 2. IaaS: virtual servers, storage and networks on rent, managed by your own IT staff — Amazon EC2. PaaS: a ready platform to build and run applications — Google App Engine. SaaS: finished software used online — Gmail, Google Docs. A school would use SaaS such as Google Docs or Sheets to prepare its routine: nothing to install, teachers can edit and view it from anywhere, and it is free or cheap.

Long 3. Soil-moisture sensors in a field can switch irrigation pumps on only when the soil is dry, saving water and electricity for farmers in the Terai; and temperature and humidity sensors in a greenhouse or poultry farm can send alerts to the farmer's phone so that conditions are corrected in time (also livestock trackers, crop-disease alerts). Challenges: devices need reliable Internet and electricity, which villages may lack; and connected devices can be hacked and the cost is high for small farmers.