All categories

3 years ago

A kettle is rated at 1 kW, 220 V. Calculate the working resistance of the kettle.

Physics

1 answer:

Anna [14]3 years ago

5 0

Explanation:

Power of electric kettle, P = 1 kW

Voltage, V = 220 V

(a) Electric power is given by the formula as follows :

$P=\dfrac{V^2}{R}$

R is resistance

$R=\dfrac{V^2}{P}\\\\R=\dfrac{(220)^2}{10^3}\\\\R=48.4\ \Omega$

(b) When connected to a 220 V supply, it takes 3 minutes for the water in the kettle to reach boiling point.

Energy supplied is given by :

$E=P\times t$

P is power, $P=\dfrac{V^2}{R}$

$E=\dfrac{V^2}{R}t\\\\E=\dfrac{(220)^2}{48.4}\times 180\\\\E=180000\ J\\\\E=180\ kJ$

You might be interested in

What direction is the net force on a falling skydiver before she reaches terminal velocity?

GarryVolchara [31]

Answer:

The net force and the acceleration on the falling skydiver is upward

Explanation:

An upward net force on a downward falling object would cause that object to slow down. the skydiver this slows down. As the speed decreases, the amount of air resistance also decreases until once more the skydiver reaches a terminal velocity.

8 0

4 years ago

the weight of a piece of stone when fully immersed in water is 18N and it displaces 4N of water. what is the weight of the stone

goldfiish [28.3K]

Answer:

Explanation:

Given parameters:

Weight of stone when immersed in water = 18N

Weight of water displaced = 4N

Unknown:

Weight of the stone in air = ?

Solution:

To solve this problem, we employ the Archimedes' principles.

It states that the upward buoyant force on a body is equal to the weight of the fluid displaced.

The weight of the water displaced is equal to the weight of the body.

So, the weight of the stone in air = 4N

4 0

3 years ago

The intensity of the sound from a certain source is measured at two points along a line from the source. The points are separate

Artemon [7]

Answer:

The source is at a distance of 4.56 m from the first point.

Solution:

As per the question:

Separation distance between the points, d = 11.0 m

Sound level at the first point, L = 66.40 dB

Sound level at the second point, L'= 55.74 dB

Now,

$L = 10log_{10}\frac{I}{I_{o}}$

$I = I_{o}10^{\frac{L}{10}} = I_{o}10^{0.1L} = 10^{- 12}\times 10^{0.1\times 66.40} = 10^{- 5.36}$

$L' = 10log_{10}\frac{I'}{I_{o}}$

$I' = I_{o}10^{\frac{L'}{10}} = 10^{- 12}\times 10^{0.1\times 55.74} = 10^{- 6.426}$

where

$I_{o} = 10^{- 12} W/m^{2}$

I = Intensity of sound

Now,

$I = \frac{P}{4\pi R^{2}}$

Similarly,

$I' = \frac{P}{4\pi (R + 11.0)^{2}}$

Now,

$\frac{I}{I'} = \frac{(R + 11.0)^{2}}{R^{2}}$

$\frac{10^{- 5.36}}{10^{- 6.426}} = \frac{(R + 11.0)^{2}}{R^{2}}$

$R ^{2} + 22R + 121 = 11.64R^{2}}$

$10.64R ^{2} - 22R - 121 = 0$

Solving the above quadratic eqn, we get:

R = 4.56 m

8 0

3 years ago

The drinking water needs of an office are met by cooling tab water in a refrigerated water fountain from 23 to 6°C at an average

Ratling [72]

Answer:

The correct option is;

Explanation:

Here we have the Coefficient Of Performance, COP given by

$COP = \frac{Q_{cold}}{W} = 3.1$

The heat change from 23° to 6°C for a mass of 10 kg/h which is equivalent to 10/(60×60) kg/s or 2.78 g/s we have

$Q_{cold}$ = m·c·ΔT = 2.78 × 4.18 × (23 - 6) = 197.39 J

Therefore, plugging in the value for $Q_{cold}$ in the COP equation we get;

$COP = \frac{197.39 }{W} = 3.1$ which gives

$W = \frac{197.39 }{3.1} = 63.674 \ J$

Since we were working with mass flow rate then the power input is the same as the work done per second and the power input to the refrigerator = 63.674 J/s ≈ 64 W.

The power input to the refrigerator is approximately 64 W.

4 0

3 years ago

Read 2 more answers

The n = 2 to n = 6 transition in the bohr hydrogen atom corresponds to the ________ of a photon with a wavelength of ________ nm

Colt1911 [192]

The energy levels of the hydrogen atom are quantized and their energy is given by the approximated formula
$E=- \frac{13.6}{n^2} [eV]$
where n is the number of the level.

In the transition from n=2 to n=6, the variation of energy is
$\Delta E=E(n=6)-E(n=2)=-13.6 ( \frac{1}{6^2}- \frac{1}{2^2} )[eV]=3.02 eV$
Since this variation is positive, it means that the system has gained energy, so it must have absorbed a photon.

The energy of photon absorbed is equal to this $\Delta E$ . Converting it into Joule,
$\Delta E=3.02 eV=4.84 \cdot 10^{-19}J$
The energy of the photon is
$E=hf$
where h is the Planck constant while f is its frequency. Writing $\Delta E=hf$ , we can write the frequency f of the photon:
$f= \frac{\Delta E}{h}= \frac{4.84 \cdot 10^{-19}J}{6.63 \cdot 10^{-34}m^2 kg/s}=7.29 \cdot 10^{14}Hz$

The photon travels at the speed of light, $c=3 \cdot 10^8 m/s$ , so its wavelength is
$\lambda = \frac{c}{f}= \frac{3 \cdot 10^8 m/s}{7.29 \cdot 10^{14}Hz}=4.11 \cdot 10^{-7}m=411 nm$

So, the initial sentence can be completed as:
The n = 2 to n = 6 transition in the bohr hydrogen atom corresponds to the "absorption" of a photon with a wavelength of "411" nm.

4 0

4 years ago

Read 2 more answers