Question 1

Why are footballs generally spherical in shape?

Accepted Answer

To ensure uniform motion. A spherical shape allows the football to move uniformly and predictably when kicked or rolled. This makes its motion smoother and more consistent during play.

Question 2

When light travels from water to air, which property remains unchanged?

Accepted Answer

Frequency. When light passes from one medium to another, its speed and wavelength change due to refraction. The frequency remains unchanged because it depends on the source of light.

Question 3

Difficulty in starting or stopping the motion of a body is due to:

Accepted Answer

Inertia. Inertia is the property of a body by which it resists any change in its state of rest or motion. That is why it is difficult to start or stop a body instantly.

Question 4

The bending of sound waves around obstacles is known as:

Accepted Answer

Diffraction. Diffraction is the bending and spreading of waves around obstacles or through openings. For sound waves, this effect is especially noticeable because sound has relatively long wavelengths.

Question 5

Why does food cook faster in a pressure cooker?

Accepted Answer

Increased boiling point of water. A pressure cooker increases the pressure above the water, which raises the boiling point of water. Since the food is cooked at a higher temperature, it cooks faster. Therefore, the correct answer is increased boiling point of water.

Question 6

Why are modern tennis rackets commonly made with graphite composites?

Accepted Answer

They reduce vibration and improve control. Graphite composites are strong, lightweight, and help absorb vibrations during impact. This improves control and makes the racket easier to handle. So, the correct option is that they reduce vibration and improve control.

Question 7

One ampere of electric current is correctly defined as:

Accepted Answer

Flow of 1 coulomb charge in 1 second. Electric current is defined as the rate of flow of electric charge. One ampere corresponds to one coulomb of charge flowing in one second.

Question 8

The SI unit ohm measures:

Accepted Answer

Electrical resistance. Ohm is the SI unit of electrical resistance. Resistance is the property that opposes the flow of electric current.

Question 9

If the speed of light in vacuum is $3 	imes 10^8$ m/s and its frequency is $6 	imes 10^{14}$ Hz, what is its wavelength?

Accepted Answer

0.5 μm. Using $\lambda = \frac{c}{f}$, we get $\lambda = \frac{3 	imes 10^8}{6 	imes 10^{14}} = 0.5 	imes 10^{-6}$ m. This equals $0.5$ μm.

Question 10

For ideal gases: 1. Molecular size is negligible. 2. There is no intermolecular attraction. 3. Inelastic collisions occur.

Accepted Answer

1 and 2 only. An ideal gas is assumed to have negligible molecular volume and no intermolecular forces. Its collisions are perfectly elastic, not inelastic, so statement 3 is incorrect.

Question 11

In the photoelectric effect: 1. Emission depends on threshold frequency. 2. Higher intensity increases the number of electrons emitted.

Accepted Answer

Both. Photoelectric emission occurs only when the incident light frequency is at least the threshold frequency. For a frequency above threshold, increasing intensity increases the number of emitted electrons, not their maximum kinetic energy.

Question 12

Which of the following statements about entropy is/are correct? 1. Entropy increases in spontaneous processes. 2. Entropy of the universe remains constant for irreversible processes.

Accepted Answer

Only 1. In spontaneous processes, the entropy of the universe increases. For irreversible processes, the entropy of the universe does not remain constant; it increases. Hence only statement 1 is correct.

Question 13

A 100 W bulb operates for 4 hours daily. Energy consumed in 25 days equals:

Accepted Answer

10 units. Power of the bulb = 100 W = 0.1 kW. Total time = 4 × 25 = 100 hours, so energy used = 0.1 × 100 = 10 kWh. Hence, the consumption is 10 units.

Question 14

Why does a person feel lighter inside an elevator that is moving downward with acceleration?

Accepted Answer

Decrease in apparent weight. A person’s feeling of weight depends on the normal reaction from the floor, called apparent weight. In a downward-accelerating elevator, this normal reaction decreases, so the person feels lighter.

Question 15

The surface tension of a liquid:

Accepted Answer

Is a scalar quantity, generally decreasing as temperature increases. Surface tension is a scalar property of a liquid. It generally decreases as temperature increases because molecular cohesion becomes weaker at higher temperatures.

Question 16

As an object is moved farther away from the Earth's surface, its gravitational potential energy relative to the surface:

Accepted Answer

Increases. Gravitational potential energy increases as an object is moved farther from the Earth's surface. This is because work is done against gravity to raise the object.

Question 17

What happens to a nucleus during alpha decay?

Accepted Answer

Proton number decreases by 2, mass number decreases by 4. In alpha decay, the nucleus emits an alpha particle, which contains 2 protons and 2 neutrons. Therefore, the atomic number decreases by 2 and the mass number decreases by 4.

Question 18

What happens to the perceived frequency when both the source and the listener move with the same speed in the same direction?

Accepted Answer

It remains unchanged. In the Doppler effect, the observed frequency depends on the relative motion between the source and the listener. If both move with the same speed in the same direction, their relative velocity is zero, so the perceived frequency remains unchanged.

Question 19

Which nuclear decay alters atomic number but not mass number?

Accepted Answer

Beta decay. In beta decay, a neutron converts into a proton or a proton converts into a neutron, changing the atomic number. The total number of nucleons remains unchanged, so the mass number does not change.

Question 20

What is the audible frequency range for the human ear?

Accepted Answer

20 – 20,000 Hz. The normal audible range for the human ear is approximately 20 Hz to 20,000 Hz. Frequencies below 20 Hz are infrasonic and above 20,000 Hz are ultrasonic.

Question 21

The color order in a secondary rainbow is:

Accepted Answer

Reversed compared to primary rainbow. A secondary rainbow is formed by two internal reflections, which reverses the order of colors compared to a primary rainbow. Therefore, the color sequence appears reversed.

Question 22

The minimum number of rays required to locate the image formed by a spherical mirror is ______.

Accepted Answer

Two. To locate the image formed by a spherical mirror, at least two rays are needed. Their reflected rays intersect at the image position, allowing the image to be determined uniquely.

Question 23

A ball is thrown vertically upward with an initial velocity of 10 m/s. Ignoring air resistance, what is the maximum height it will reach? (Assume $g = 9.8\,	ext{m/s}^2$)

Accepted Answer

5.10 m. At the maximum height, the final velocity becomes zero. Using $0 = u^2 - 2gh$, we get $h = \frac{u^2}{2g} = \frac{100}{19.6} \approx 5.10$ m.

Question 24

A person needs spectacles with a power of -2.5 D. This indicates that the person is suffering from:

Accepted Answer

Myopia and needs a diverging lens. A negative power indicates a diverging or concave lens. Such lenses are used to correct myopia, where distant objects appear blurred.

Question 25

Two resistors, one with a resistance of 2 ohms and the other with a resistance of 4 ohms, are connected in parallel to a 6-volt battery. What is the total current flowing through the circuit?

Accepted Answer

4.5 Amperes. For resistors in parallel, the equivalent resistance is $R = \frac{R_1R_2}{R_1+R_2} = \frac{2\times4}{2+4} = \frac{8}{6} = \frac{4}{3}\,\Omega$. Using Ohm’s law, total current $I = \frac{V}{R} = \frac{6}{4/3} = 4.5\,A$.

Question 26

What does an alpha particle represent in alpha decay?

Accepted Answer

Helium. An alpha particle is essentially a helium nucleus, consisting of 2 protons and 2 neutrons. That is why alpha decay reduces the atomic number by 2 and mass number by 4.

Question 27

A sound wave travels from air into water. How do its speed and wavelength change?

Accepted Answer

Speed increases, wavelength increases.. Sound travels faster in water than in air, so its speed increases on entering water. Since frequency remains constant, wavelength also increases because $v = f\lambda$.

Question 28

The value of g (acceleration due to gravity) is minimum at:

Accepted Answer

The center of the Earth. The acceleration due to gravity decreases as we move toward the center of the Earth and becomes zero at the center. Hence, it is minimum there.

Question 29

Why are footballs typically made in a spherical shape?

Accepted Answer

To ensure uniform and predictable motion. A spherical shape gives the ball uniform behavior in all directions, so its motion is more predictable during play. This makes passing, kicking, and rolling consistent.

SSC CGL (Prelims) General: Physics questions with solutions

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