Question Discussion & Solution

The correct answer is 37 °C.

Key Points

• The normal temperature of the human body is 37 °C.
• A temperature above 100.4 °F(38°C) most often means you have a fever caused by an infection or illness.
• Normal human body temperature is the prototypical temperature range found in humans.
• The normal human body temperature border is typically stated as 36.5–37 °C (97.7–98.6 °F).
• Human body temperature changes, it depends on gender, age, time of day, exertion level, health status, what part of the body the measurement is taken at, state of consciousness (waking, sleeping, sedated), and emotions.
• Body temperature is kept in the normal range by thermoregulation, in which adaptation of temperature is triggered by the central nervous system.

1) × and ÷

Given statement: 46 ÷ 2 -­ 7 × 3 + 5 = 39

On interchanging the above signs,

46 × 2 ­- 7 ÷ 3 + 5

= 46 × 2 ­- 2.33 + 5

= 92 ­- 2.33 + 5

= 97 -­ 2.33

= 94.67 ≠ 39

2) ­- and ×

Given statement: 46 ÷ 2 -­ 7 × 3 + 5 = 39

On interchanging the above signs,

46 ÷ 2 × 7 -­ 3 + 5

= 23 × 7 -­ 3 + 5

= 161 ­- 3 + 5

= 166 ­- 3

= 163 ≠ 39

3) + and ×

Given statement: 46 ÷ 2 -­ 7 × 3 + 5 = 39

On interchanging the above signs,

46 ÷ 2 7 + 3 × 5

= 23 ­- 7 + 3 × 5

= 23 ­- 7 + 15

= 38 7

= 31 ≠ 39

4) + and ­-

Given statement: 46 ÷ 2 -­ 7 × 3 + 5 = 39

On interchanging the above signs,

46 ÷ 2 + 7 × 3 ­- 5

= 23 + 7 × 3 ­- 5

= 23 + 21 ­- 5

= 44 -­ 5

= 39

All except Yosemite National Park are in India. Yosemite National Park is in USA.

The correct answer is Mirage.

• To a distant observer, the light appears to be coming from somewhere below the ground.
• The observer naturally assumes that light is being reflected from the ground, say, by a pool of water near the tall object.
• Such inverted images of distant tall objects cause an optical illusion to the observer.
• This phenomenon is called a mirage.
•  The optical illusion which occurs mainly in the desert during hot summer is based on the principle of TIR i.e total internal reflection.
• This type of mirage is especially common in hot deserts.

Additional Information

• Total Internal Reflection (TIR): When a ray of light goes from denser to the rarer medium it bends away from the normal and as the angle of incidence in denser medium increases, the angle of refraction in the rarer medium also increases and at a certain angle, angle of refraction becomes 90°, this angle of incidence is called critical angle (C).
• When the Angle of incidence exceeds the critical angle then the light ray comes back into the same medium after reflection from the interface. This phenomenon is called Total internal reflection (TIR).
• Conditions for TIR: 
  1. The ray must travel from denser medium to rarer medium.
  2. The angle of incidence 'i' must be greater than the critical angle C.

All terms are arranged in increasing order:

Pebble < Rock < Mountain

Similarly,

Lake < River < Sea