Physics Questions & Answers - Free Online Practice

1,366.

What is the angle of dip at the magnetic equator

\( 45^{\circ} \)

\( 0^{\circ} \)

\( 90^{\circ} \)

\( 180^{\circ} \)

Correct answer is B

The angle of dip dip is the angle which the resultant earth's magnetic field makes with the horizontal.
At the magnetic equator, which is entirely along the horizontal this angle is zero

1,367.

A bread toaster uses a current of 4A when plugged in a 24oV line. it takes 1 minute to toast slices of bread. what is the energy consumed by the toaster

5.76 x 10⁴J

1.60 x 10⁴J

3.60 x 10³J

1.60 x 10²J

View answer & explanation

Correct answer is A

Electrical Energy = IVt
= 4 x 240 x (1 x 60)
= 57600J
= 5.76 x 10⁴J

1,368.

Find the frequencies of the first three harmonics of a piano string of length 1.5m, if the velocity of the wave on the string is 120ms^-1

40Hz, 80Hz, 120Hz

80Hz, 160Hz, 240Hz

180Hz, 360Hz, 540Hz

369Hz, 180Hz, 90Hz

View answer & explanation

Correct answer is A

in vibrations in string, the fundamental frequency happens to be the first harmonic, and is given as

f₀ = V/2l.

Where V = Velocity of the sound wave, I = Length of the string.

The second harmonic is the first overtone given by

f₁ = V/l = 2f₀ ;

and the third harmonic happens to be the second overtone, given by

f₂ = 3V/2l = 2f₀.

Thus if V = 120m/s and l = 1.5m
Thus f₁ = 2f₀ = 2 x 40 = 80Hz
Thus f₂ = 3f₀ = 3 x 40 = 120Hz
Thus we have in order, 40Hz, 80Hz, 120Hz