a. What does a transformer do? b. Interpreting Diagrams . What is the difference between a step-up transformer and a step-down transformer? c. Why do some appliances have step-down transformers built into them?

A model-train transformer plugs into 120 V ac, and draws 0.75 A while supplying $15 ~\mathrm{A}$ to the train.

(a) What voltage is present across the tracks? (b) Is the transformer step-up or step-down?

How would the illustration look if it were showing a step-down transformer?

A preheater involves the use of condensing steam at $100^{\circ} \mathrm{C}$ on the inside of a bank of tubes to heat air that enters at 1 atm and $25^{\circ} \mathrm{C}$. The air moves at 5 m/s in cross flow over the tubes. Each tube is 1 m long and has an outside diameter of 10 mm. The bank consists of 196 tubes in a square, aligned array for which $S_{T}=S_{L}=15 \mathrm{mm}$. What is the total rate of heat transfer to the air? What is the pressure drop associated with the airflow?

Is this transformer a step-up transformer or a step-down transformer?

A model-train transformer plugs into $120~\mathrm{V}$ ac and draws $0.35$ A while supplying $6.8 \mathrm{~A}$ to the train. Is the transformer step-up or step-down?

A step-down transformer is used for recharging the batteries of portable devices. The turns ratio $N_2/N_1$ for a particular transformer used in a CD player is 1:13. When used with 120-V (rms) household service, the transformer draws an rms current of 250 mA. Find the rms output voltage of the transformer

Consider an array of vertical rectangular fins which is to be used to cool an electronic device mounted in quiescent, atmospheric air at $T_{\mathrm{x}}=27^{\circ} \mathrm{C}$. Each fin has $L=20 \mathrm{~mm}$ and $H=150 \mathrm{~mm}$ and operates at an approximately uniform temperature of $T_s=77^{\circ} \mathrm{C}$. Viewing each fin surface as a vertical plate in an infinite, quiescent medium, calculate the rate of heat transfer from a fin by free convection. Comment on the effect of boundary layer formation on specifying the spacing between fins.

The general form of the Stefan-Maxwell equation for mass transfer of species i in an n-component ideal gas mixture along the z-direction for flux is given by

$$\frac{d y_{i}}{d z}=\sum_{j=1, j \neq i}^{n} \frac{y_{i} y_{j}}{D_{i j}}\left(\nu_{j}-\nu_{i}\right)$$

Show that for a gas-phase binary mixture of species A and B, this relationship is equivalent to Fick's rate equation:

$$N_{A, z}=-c D_{A B} \frac{d y_{A}}{d z}+y_{A}\left(N_{A, z}+N_{B, z}\right)$$

A model-train transformer plugs into $120~\mathrm{V}$ ac and draws $0.35 \mathrm{~A}$ while supplying $6.5 \mathrm{~A}$ to the train. Is the transformer step-up or step-down?

A step-down transformer is used for recharging the batteries of portable devices such as tape players. The turns ratio inside the transformer is $13: 1$ and it is used with $120-\mathrm{V}$ (rms) household service. If a particular ideal transformer draws $0.350 \mathrm{~A}$ from the house outlet, what are (a) the voltage and (b) the current supplied to a tape player from the transformer? (c) How much power is delivered?

A model-train transformer plugs into 120-V ac and draws 0.35 A while supplying 7.5 A to the train. Is the transformer step-up or step-down?

Why do some appliances have step-down transformers built in?

How would the illustration look if it were showing a step-down transformer?