Question

9 Two resistances 2Ω and 3Ω are in parallel. The combination is in series with 1.5Ω resistance and a power supply of voltage V. There is a current of 3A through the 2Ω resistance. What are the values of the current I delivered by, and the voltage V across the power supply? (a) 3A and 10.5V (b) 4A and 9V (c) 4A and 12V (d) 12A and 18V
11 A current of 0.5A flowing through a wire produces 21J of heat in 1/2 min. The resistance of the wire is ----------- ohms to 1 place of decimal? (a)2.8Ω (b)3.2Ω (c)1.4Ω (d) 4.6Ω
14 The physical phenomenon which accounts for apparent depth of a pool of water is called? (a)waves (b) polariztion (c) diffraction (d) refraction
15 The ------------ of the eye plays an equivalent role of the screen in optical experiments? (a) lens (b) iris (c) optic nerve (d) retina

Answer 1

Answer on Question #51847-Physics-Optics

9 Two resistances $2\Omega$ and $3\Omega$ are in parallel. The combination is in series with $1.5\Omega$ resistance and a power supply of voltage V. There is a current of 3A through the $2\Omega$ resistance. What are the values of the current I delivered by, and the voltage V across the power supply?

(a) 3A and 10.5V (b) 4A and 9V (c) 4A and 12V (d) 12A and 18V

Solution

The voltage across the resistor with resistance $2\Omega$ from the Ohm's law:

$$I _ {1} = \frac {U _ {1}}{R _ {1}}; U _ {1} = R _ {1} I _ {1} = 2 \Omega \cdot 3 A = 6 V.$$

Because the resistance connected in parallel, they have the same voltage:

$$U _ {1} = U _ {2} = 6 V,$$ $$I _ {2} = \frac {U _ {2}}{R _ {2}} = \frac {6 V}{3 \Omega} = 2 A.$$

The total current in the circuit is the sum of the currents through the two resistances $R_{1}$ and $R_{2}$ is

$$I = I _ {1} + I _ {2} = 2 A + 3 A = 5 A.$$ $$U _ {3} = I R _ {3} = 5 A \cdot 1. 5 \Omega = 7. 5 V.$$

The voltage across the power supply:

$$U _ {p o w e r} = U _ {3} + U _ {1} = 7. 5 V + 6 V = 1 3. 5 V.$$

Answer: 5A and 13.5V.

11 A current of 0.5A flowing through a wire produces 21J of heat in 1/2 min. The resistance of the wire is --- ohms to 1 place of decimal?

(a) $2.8\Omega$ (b) $3.2\Omega$ (c) $1.4\Omega$ (d) $4.6\Omega$

Solution

By the Joule's law:

$$Q = I ^ {2} R t$$

Where $Q$ – heat, $t$ – time in seconds, $R$ – wire resistance

$$R = \frac{Q}{I^2 t} = \frac{21\mathrm{J}}{(0.5\mathrm{A})^2 \cdot 30\mathrm{s}} = 2.8\Omega.$$

Answer: (a) $2.8\Omega$.

14 The physical phenomenon which accounts for apparent depth of a pool of water is called?

(a) waves (b) polarization (c) diffraction (d) refraction

Solution

The physical phenomenon which accounts for apparent depth of a pool of water is called refraction.

Answer: (d) refraction.

15 The ________ of the eye plays an equivalent role of the screen in optical experiments?

(a) lens (b) iris (c) optic nerve (d) retina

Solution

The retina of the eye plays an equivalent role of the screen in optical experiments.

The optics of the eye create an image of the visual world on the retina (through the cornea and lens), which serves much the same function as the film in a camera.

Answer: (d) retina.

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