ECAT MCQs

The sound travels to the wall and back, so distance to wall is vt/2.
340×0.6/2 = 102 m.

A converging lens brings paraxial parallel rays to its principal focus.
The focal length is positive under the common sign convention.

In-phase displacements add constructively.
The resultant amplitude is 3+2 = 5 cm.

A diverging lens causes rays to separate.
Their backward extensions meet at a virtual focal point.

Opposite-phase amplitudes subtract.
The resultant amplitude is |5-3| = 2 cm.

For the fundamental, the string length is half a wavelength.
λ=2L=2.4 m.

The fundamental wavelength is 2L=1.5 m.
F=v/λ=300/1.5 = 200 Hz.

For an open pipe, fundamental wavelength is 2L=1.7 m.
F=340/1.7 = 200 Hz.

For a closed pipe, fundamental wavelength is 4L=3.4 m.
F=340/3.4 = 100 Hz.

Reflection changes the direction of light at a boundary.
The incident and reflected rays remain in the same medium.

Angles are measured from the normal to the surface.
The incident ray, reflected ray, and normal lie in one plane.

Refraction occurs because wave speed changes across a boundary.
The frequency remains constant while wavelength changes.