Explanation

• The Doppler Effect is the change in the observed frequency of sound due to the relative motion between the source and the observer.
• If the source and observer move toward each other, the observed frequency increases.
• If they move away from each other, the observed frequency decreases.
• A common example is the changing pitch of an ambulance siren as it passes by.

Last verified on 02-09-2026

Explanation

• Ibn al-Haytham presented the theory of reflection and refraction of light.
• He is also known as Alhazen.
• His work, particularly his "Book of Optics", is titled Kitab al-Manazir, written during 1011–1021.
• Born: c. 965 (c. 354 AH) Basra, Buyid Emirate
• Died: c. 1040 (c. 430 AH)[1] (aged around 75) Cairo, Fatimid Caliphate

Last verified on 02-09-2026

Explanation

• Pressure is a scalar quantity.
• Pressure can be defined as the force acting per unit area.
• The unit of pressure is N/m² (Newton per square meter).
• It is also called a pascal (Pa).
• In SI base units: kg⋅m−1⋅s−2
• Derivation from other quantities: p = F / A
• Dimensional unit: M L^−1 T^-2.

Explanation

The particle's path is a helix.

Reasoning:

• Velocity has two components:
  • Parallel to the fields → electric force accelerates it along the axis
  • Perpendicular to the fields → magnetic force makes it circle around the axis
• Combined → helical path (with changing pitch as it speeds up/slows down)

Explanation

• Length, mass, and time are fundamental physical quantities.
• They can be measured using standard units.
• SI units are the metre for length, the kilogram for mass, and the second for time.

Explanation

Formula:  

Mean = Sum of observations / Number of observations  

Given:  

Mean = 50  

Number of observations = 10  

Sum of observations = Mean _ Number of observations  

= 50 _ 10  

= 500

Last verified on 11-07-2026

Explanation

• Humidity is the measure of the amount of moisture (water vapour) in the air.
• A hygrometer is used to measure relative humidity.
• A psychrometer is an example of a hygrometer.
• Relative humidity tells us the ratio of water vapour present in the air compared with the maximum amount the air can hold at a given temperature.
• Humidity is commonly expressed as a percentage (%).

Last verified on 23-08-2026

Explanation

• Venus comes closest to Earth when it is between Earth and the Sun.

• Minimum distance: about 24 million miles (≈ 38 million km).

• This close approach occurs roughly every 584 days.

Additional Information:

• Mercury can be about 33 million miles away when Venus is on the far side of the Sun.

Last verified on 17-01-2026

Explanation

Given:

• Diameter, $d=19mm=0.019m$
• Length, $L=1.51m$
• Tensile force, $P=150kN=150,000N$
• Modulus of Elasticity, E=200GPa=200×109N/m^2

Formula:

δ=PL/AE​

1. Cross-sectional area:

A=πd^2​/4

A=π(0.019)^2/4 ​=0.0002835 m^2

2. Axial elongation:

δ=150000×1.51/ 0.0002835×200×10^9

$$\delta =0.003994m$$

$$\delta =3.99mm$$

Answer: 3.99mm≈4mm​

Explanation

• Earthquakes generate dynamic/inertial forces in a dam.
• These forces can significantly increase the shear stress within the dam.
• Earthquake loading is therefore considered in the seismic design of dams.