25 An electromagnetic wave in free space has a frequency of 2.5  10 14 Hz.Which region of the electromagnetic spectrum includes this frequency?A infraredB microwaveC ultravioletD X-ray26 Two polarising filters are placed next to each other so that their planes are parallel.The first polarising filter has its transmission axis at an angle of 50 to the vertical.The second polarising filter has its transmission axis at an angle of 20 to the vertical. The anglebetween the transmission axes of the two polarising filters is 30A beam of vertically polarised light of intensity 8.0 W m–2 is incident normally on the first polarisingfilter.What is the intensity of the light that is transmitted from the second polarising filter?A zero B 2.5 W m–2 C 2.9 W m–2 D 6.0 W m–227 A stationary wave on a stretched string is set up between two points P and T.PQRSTvibratorWhich statement about the stationary wave is correct?A Point R is at a node.B Points Q and S vibrate in phase.C The distance between P and T is three wavelengths.D The wave transfers energy from P to T.

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25. The frequency of the electromagnetic wave is 2.5 x 10^14 Hz. This frequency falls within the visible light to ultraviolet range of the electromagnetic spectrum. Therefore, the correct answer is C. Ultraviolet.

26. The intensity of light transmitted through two polarizing filters is given by Malus's law, which states that the intensity I of the transmitted light is directly proportional to the square of the cosine of the angle θ between the transmission axes of the filters. The angle between the filters is 30 degrees. So, the intensity I of the light transmitted from the second filter is I = I0 * cos^2(θ) = 8.0 W/m^2 * cos^2(30) = 8.0 W/m^2 * (0.866)^2 = 6.0 W/m^2. Therefore, the correct answer is D. 6.0 W/m^2.

27. A stationary wave on a stretched string is set up between two points P and T. The points at maximum amplitude (maximum displacement from the rest position) are called antinodes, and the points with zero amplitude (no displacement) are called nodes. In the given diagram, points P, R, and T are nodes, and points Q and S are antinodes. Therefore, the correct answer is B. Points Q and S vibrate in phase.